Plant-Soil Interactions of Fragmented Habitats

INTRODUCTION

This blog post will be the final in my quasi-series on habitat fragmentation. And I would like to dedicate this last post to plant-soil interactions in disturbed habitats. It is a topic that has not been extensively studied, but I had a few questions: does soil in a fragmented forest differ from the soil in a continuous forest? Is disturbed soil more nutrient dense or is is worse for the plants living in that soil? How does the soil affect with nearby plants, let alone an environment under stress such as a forest or grassland made up of broken pieces? Well, the answer to a lot of these questions are kind of like the answer your parents gave you when you were a little too young to know the "real" answers: it's complicated. And these answers are complicated because there are a kaleidoscope of biotic and abiotic factors that come into play when discussing things like the birds and the bees or something less awkward like plant-soil interactions in fragmented habitats. Because even if we do find significant changes in soil composition at a site, those changes cannot be solely responsible for above ground changes (Tipton et al. 2016). Luckily, no one reading this is too young to know about plant-soil interactions. Throughout this blog post I will discuss the ways in which plant-soil interactions have an impact on habitat fragmentation. I will be looking at these interactions through plant-soil feedback, the effects of fragment size on plant-soil interactions, and finally the overall effects on plant growth.


PLANT-SOIL FEEDBACK
Pizano et al. tells us that "plants are constantly influencing, and being influenced by highly diverse soil biota-containing organisms that exert neutral, beneficial, or antagonistic effects on plants" (Pizano et al. 2014). But we want to know if the change is a positive one or a negative one. Positive feedback is when a plant grows best in its native soil biota, and it can mean that the helpful organisms in the soil outnumber the harmful organisms. Negative feedback can mean the exact opposite, and potentially a parasite or pathogen in the native soil could bring major harm to the plants. This usually happens when one plant species has dominated the landscape for so long, an antagonistic organism has time to build up (Pizano et al. 2014). According to a study conducted by Pizano et al., and one other source from my collected research, the life history of a plant in addition to a lot of abiotic and biotic factors determine whether feedback of plant-soil interactions will be positive, negative, or neutral (Grilli et al. 2014). In this same study, for example, fast growing plants from forest fragments did not fare as well in native soil, however when slow growing plants from the same fragments were placed in their native soil they had significant positive feedback (Grilli et al. 2014). This could have implications that quickly growing species might have an advantage in fragmented or disturbed environments if they can adapt and spread quickly to foreign soils. Next we will see if fragment size really affects plant-soil interactions.

DOES FRAGMENT SIZE AFFECT PLANT- SOIL INTERACTIONS?
To look at the potential outcomes of plant-soil interactions in a fragmented forest, Grilli et al. conducted an experiment and found that "soil fungi from small forest fragments promoted lower rates of mycorrhizal colonization than soil form large forest fragments" (Grilli et al. 2014). They also found that plant growth was being stunted by arbuscular micorrhizal networks, and those negative effects on growth could have direct effects on community composition and population dynamics. However, fragment size did not have much of a hold on plant-soil interactions, as did the regional climate and abiotic effects.

In another study, the size of the fragment did have significant effects on the soil (Flores-Renteria et al. 2015). Unlike the paper above, this experiment found that soil composition was largely influenced by the size of the fragment and less on the regional climate. In the smaller fragments, there was greater soil nutrients. However, in this paper, the researchers found that plants were more productive in the smaller fragments than in the larger ones, because the large content of organic matter in the small fragments allowed soil to retain more water and therefore, "increased the functionality of the plant-soil-microbial system" (Flores-Renteria et al. 2015). In the figure below, we can see simulaneous relationships of bacterial richness, fungal richness, and fragment size (Flores-Renteria et al. 2015).


SOIL VS. PLANT GROWTH
Now we're going to look at how soil differences in fragmented habitats affect plant growth. Just to recap: habitat fragmentation can undermine the integrity of what was a seemingly stable ecosystem. Some factors affecting forest fragments include a greater chance of interactions with light, heat, and wind. Additionally, many species of plants are adapted to a small environmental niche, and the change in soil quality due to habitat fragmentation and edge effects can result in decreased plant fitness according to 4 papers (Wardle 2006; Mangan et al. 2004; Cojoc et al. 2016; Pizano et al. 2014). According to two papers, multiple species of plants showed negative correlation between plant success and increased soil nutrient content in a disturbed habitat (Tsaliki et al. 2010; Tipton et al. 2016). And according to 2 papers,  plants show decreased success in fragmented environments where soil has been enriched (Mangan et al. 2004; Tsaliki et al. 2010). Tsaliki et al. believes this could be due to the fact that some species of plant have adapted to very low-nutrient soils, and in these dry, acidic environments they thrive; or, they can simply "lose their competitive advantage when nutrients are added" (Tsaliki et al. 2010).

TAKEAWAYS
I discussed the ways in which plant-soil interactions have an impact on habitat fragmentation, additionally, I looked at these interactions through plant-soil feedback, the effects of fragment size on plant-soil interactions, and finally the overall effects on plant growth. In conclusion, plant-soil interactions in fragmented habitats are complicated. More experiments need to be conducted looking at the intersection of soil, plants, and disturbed habitats to more extensively understand the interactions between them in varying ecosystems as well as better understanding to how these interactions affect the environment as a whole.


 WORKS CITED

Cojoc, Emilia Ionela, Carmen Postolache, Bogdan Olariu, and Carl Beierkuhnlein. "Effects of anthropogenic fragmentation on primary productivity and soil carbon storage in temperate mountain grasslands." Environmental Monitoring and Assessment 188.12 (2016): n. pag.

Flores-Rentería, Dulce, Jorge Curiel Yuste, Ana Rincón, Francis Q. Brearley, Juan Carlos García-Gil, and Fernando Valladares. "Habitat Fragmentation can Modulate Drought Effects on the Plant-soil-microbial System in Mediterranean Holm Oak (Quercus ilex) Forests." Microbial Ecology 69.4 (2015): 798-812.

Grilli, G., C. Urcelay, M. S. Longo, and L. Galetto. "Mycorrhizal fungi affect plant growth: experimental evidence comparing native and invasive hosts in the context of forest fragmentation." Plant Ecology 215.12 (2014): 1513-525.

Mangan, Scott A., Ahn-Heum Eom, Gregory H. Adler, Joseph B. Yavitt, and Edward A. Herre. "Diversity of arbuscular mycorrhizal fungi across a fragmented forest in Panama: insular spore communities differ from mainland communities." Oecologia 141.4 (2004): 687-700.
Pizano, Camila, Scott A. Mangan, James H. Graham, and Kaoru Kitajima. "Habitat-specific positive and negative effects of soil biota on seedling growth in a fragmented tropical montane landscape." Oikos 123.7 (2014): 846-56.

Tipton, Alice G., Nicole E. Miller-Struttmann, and Candace Galen. "Finding partners in a habitat mosaic: Patch history and size mediate host colonization by arbuscular mycorrhizal fungi." Ecosphere 7.11 (2016): n. pag.
Tsaliki, M., and M. Diekmann. "Effects of habitat fragmentation and soil quality on reproduction in two heathlandGenistaspecies." Plant Biology (2009): n. pag.

Wardle, David A. "The influence of biotic interactions on soil biodiversity." Ecology Letters 9.7 (2006): 870-86.

Images:
https://foodtank.com/wp-content/uploads/2013/10/global_soil_week.jpg

Nurse Plants: Can They Restore the World One Fragment at a Time?

Did you ever watch the show, "Extreme Couponers" on TLC? I am not sure if it still comes on, but if you have not seen it context clues should tell you that it was great television. Needless to say it is a fascinating display of human resourcefulness, and definitely not exploitation of unsuspecting mothers for mass consumption. Besides that, these people sort for hours and cut coupons that result in them bringing home 7 carts of groceries for less than $18.00 all because their family fell on hard times and couponing became a way to make ends meet. So, for them, couponing provided a cozy cushion to support their family in a time of desperate need. And in this way, nurse plants are kind of like coupons. Nurse plants provide nutrients, shelter, and protection in stressful environments. They can be introduced in extreme habitat conditions to help restore an ecosystem, like those suffering from habitat fragmentation. In this blog post I will discuss the ways in which nurse plants can help restore fragmented habitats as well as potential downfalls of these particular plant-plant interactions.

Plant-plant interactions can be competitive, mutualistic, or even parasitic. Most often when we think of plants interacting in the same space we think competition, especially when that space has been disturbed and destroyed leaving very little behind. However, there is research that suggests that plants can facilitate growth of nearby plants and actually work together under higher levels of abiotic stress (Anthelme, Gómez-Aparicio, & Montúfar 2014; Stachowicz 2001; Aerts, et al. 2006). I dug through 8 articles that talk about these facilitative plant-plant interactions in fragmented habitats. Results from the research tells us that for the most part nurse plants can be an extremely helpful tool in the restoration process, but there are many factors that come into play that can affect whether the outcome is positive or negative.




NURSE EXPECTATIONS 
Nurse plants can have major impacts on biodiversity and community structure through positive plant-plant interactions according to all 8 articles. They serve important functions (as you can see in the chart below) within environments that have experienced lots of stress or have been disturbed by human inflicted habitat fragmentation.

From the research that is currently available, we can read about all of the benefits like: reducing soil erosion, protecting seedlings, reducing herbivory, and providing lots of shade in the face of more extreme weather patterns (Stachowicz 2001; Howe & Miriti 2004). For instance, if the nurse plant is very popular with the nearby pollinators, some of those pollinators just might stop by the little guys and further help the growth of the facilitated species. 1 of the 8 articles reported that there was "high community structure" in the patches where nurse plants were implemented, and the results showed a positive relationship in patches with a focal nurse plant species than in those without (Nuñez et al. 1999). The study also showed a steady increase in diversity over time (Nuñez et al. 1999).

It has been stated in two of the studies, that the shade from the the nurse plant provides lots of shade especially in very dry conditions where seeds have shelter from the sun and can have a greater chance for germination (Valladares & Gianoli 2007; Howe & Miriti 2004). Anthelme, Gómez-Aparicio, & Montúfar report on results from experiments in the Andean tropical forest they saw that seedlings left without a nurse plant or artificial shade were all dead within 10 months. But the results from nurse tussock grass caused reduced soil temperature and composition which made for soil more suitable to grow in; the nurse grass also caused reduced stress from lack of water and reduced stress from herbivory (Anthelme, Gómez-Aparicio, & Montúfar 2014).

Introducing a focal nurse plant changes soil composition, which can lead to richer soil and increase biodiversity over time (Nuñez et al. 1999). Restoring these patches could increase connectivity and promote more spread of plant species and increase biodiversity. However, one study did find that facilitative effects may not be long term, because the positive effects began to fade with time (Anthelme, Gómez-Aparicio, & Montúfar 2014).


 

FACILITATION VS. COMPETITION
So, we can see from these articles that nurse plants can have a major impact on a fragmented ecosystem. Now, we will look at potential downfalls of the nurse plant. While facilitation is a fascinating display of plant-plant interactions, it can sometimes be too much of a good thing. You can be an extreme coupon-er (is that a word?) but at some point you are just spending way too much money on toilet paper, deli-meat, and jello than you actually need, and the cost outweighs the benefits. The 200 packs of chocolate pudding that you purchased for your family of 5 to snack on will most likely expire before it can be consumed, and that is not an example of resourcefulness, that is wasteful.

In fact, 2 of the 8 articles I reviewed found that in some experiments, nurse facilitation was not advantageous at all (Galindo, et al. 2017; Padilla & Pugnaire 2006). Some of these cases reported negative effects after introducing nurse plants. 1 of the 8 articles reported that nurse plants placed can out-compete native species once both plants have grown to a stable size (Galindo, et al. 2017). Padilla and Pugnaire found in their research that nurse plants in fragmented habitats were advantageous for the facilitated plant in "optimal conditions," but when a drought came, all the plants died (Padilla & Pugnaire 2006). They also discovered that in fertile soils, the nurse plants depleted the land of its nutrients and there was less biomass (Padilla & Pugnaire 2006). From studies like this, we can see that there may not be any advantages from nurse plants in restoring habitats.

TAKEAWAYS
To find a one size fits all answer to the problem surrounding habitat fragmentation would be wonderful, but sadly it is not realistic. There are far too many plant responses in addition to the varying conditions of each ecosystem to take into account; so, it is best to combine different techniques for the most productive outcome. It is so imperative that "caveats regarding species and site characteristics" are taken into account because they could have a major impact on the productivity and restoration of a fragmented habitat (Padilla & Pugnaire 2006).




WORKS CITED

Aerts, Raf, Wouter Maes, Eva November, Aklilu Negussie, Martin Hermy, and Bart Muys. "Restoring dry Afromontane forest using bird and nurse plant effects: Direct sowing of Olea europaea ssp. cuspidata seeds." Forest Ecology and Management 230.1-3 (2006): 23-31.

Anthelme, Fabien, Lorena Gómez-Aparicio, and Rommel Montúfar. "Nurse-based restoration of degraded tropical forests with tussock grasses: experimental support from the Andean cloud forest." Journal of Applied Ecology 51.6 (2014): 1534-543.

Galindo, Víctor, Zoraida Calle, Julian Chará, and Inge Armbrecht. "Facilitation by pioneer shrubs for the ecological restoration of riparian forests in the Central Andes of Colombia." Restoration Ecology (2017).

Howe, Henry F., and Maria N. Miriti. "When Seed Dispersal Matters." BioScience 54.7 (2004): 651.

Nuñez, Cecilia I., Marcelo A. Aizen, and Cecilia Ezcurra. "Species associations and nurse plant effects in patches of high-Andean vegetation." Journal of Vegetation Science 10.3 (1999): 357-64.

Padilla, Francisco M., and Francisco I. Pugnaire. "The role of nurse plants in the restoration of degraded environments." Frontiers in Ecology and the Environment 4.4 (2006): 196-202.

Stachowicz, John J. "Mutualism, Facilitation, and the Structure of Ecological Communities." BioScience 51.3 (2001): 235.

Valladares, Fernando, and Ernesto Gianoli. "How Much Ecology Do We Need to Know to Restore Mediterranean Ecosystems?" Restoration Ecology 15.3 (2007): 363-68.


  
Picture 1: http://rainforests.mongabay.com/facts/rainforest-facts.html

Picture 2: https://www.researchgate.net/figure/265053296_fig1_Figure-1-A-conceptual-framework-for-the-abiotic-and-biotic-mechanisms-of-nurse-plant

Pollination Disruption in Fragmented Habitats

The year is 2042, Oprah Winfrey is president of the United States, the balance between man and Earth has been rightfully restored, and it has been a long two years since you graduated from university. Only one of these statements seems unrealistic, and I can tell you it is NOT the one about Oprah. Your mother is recently very proud of you because you aren't sleeping on your twin-sized Buzz Lightyear sheets at home anymore. You have secured a respectable job that allows you to pay back those hefty student loans in addition to putting some cash towards a proper vacation once the summer rolls around. A lot of hard work and sleepless nights have gone into the past few years of trying to get to where you are now, so you want to take a vacation to relax and unwind. A national park camping trip in California sounds nice, but so does a tropical beach trip in Cambodia. Getting away from the never-ending stress of everyday life to the serene outdoors sounds like the sweetest- and most rewarding- dream. However, the sad truth about the year 2042 is that many vacation destinations have fallen victim to steady habitat fragmentation and destruction due to growing popularity of Earth's natural wonders. So, while you wanted to zip-line through a tropical forest in the middle of July, you could potentially just be zip-lining over: log cabins, winding roads, themed restaurants, and the tiny remnants of what is left of that tropical forest.

Anthropogenic habitat fragmentation, as I discussed in my first post, is happening at a more rapid rate than effected populations can adapt to (Lienert, J. 2004) and has major impacts on plant-pollinator interactions. Fragmentation can put a major damper on the health and biodiversity most ecosystems are trying to maintain. This has been shown especially true when reviewing the important interactions between pollinators and their plants. So, throughout this paper I will discuss how fragmented habitats impact pollination patterns.

LONG DISTANCE RELATIONSHIPS
Long distance relationships are hard. Whether your (human) partner lives halfway across the country or (your plant partner) is just across I-40 and Turkey Creek. When I think of pollinators and land disruption, the first thing that pops into my mind is the increase in distance that the pollinator will have to travel to get these plants. Three of the studies relayed that bees, butterflies, and moths can fly over long distances to food sources. However, there was a study that noted male bees could not make it across a fragmented landscaped of 100 meters, so the data really varies from study to study (Didham et al. 1996). Below the graph on the left depicts pollinator visits in two different areas of a forest (Valdivia 2011). We can see that in this study there were far less visits at the edges of the fragmented forest than in the connected mainland. On the right we can see lack of fruit and seed growth in plants depending on their location in a fragmented forest (Valdivia 2011).
 
Likewise, three of the papers showed a decrease in "the most common pollinator" and as you got closer to the edges of these fragmented landscapes, the plants there were visited less often and in one study these plants exhibited a smaller fruit and seed set (Steffan-Dewenter, Ingolf and Teja, Tscharntke. 2002). Carlos Valdivia noted from his study that plants at the edges of the forest patch have larger petals and foliar displays than flowers on the mainlands, and even with a larger display, they still receive less traffic. The effects of fragmentation and lack of pollination over patches of habitat do not bode well for plant-pollinator interactions.

SPECIALIZATION IN PLANT + POLLINATOR INTERACTION
 

Plants are pollinated in many different ways. They can cross-pollinate by wind, water, or use animals for fertilization. Wind and water pollination make up a much smaller percentage by which plants reproduce, but they are worth mentioning. The reason that animal or insect pollination is particularly cardinal is because plants and their pollinators have co-evolved as long as plants and animals have interacted, and in this fact, many plants have intricate structures made especially for a particular type of pollinator. Plants are often visited by multiple species of pollinator, "but a critical level of pollinator species richness is needed for successful pollination and maintenance of diverse plant communities" (Steffan-Dewenter, Ingolf and Teja, Tscharntke. 2002). And according to one of the studies, if a plant is thriving from the pollination of a small set of species, it would be more difficult for that plant and that pollinator to survive in a fragmented environment (Skogen et al. 2016).

If a species of plant is pollinated by a specialized insect or animal, then the problem of separation and decline in plant number can elicit a significant change in pollinator population number. These pollinators require a certain amount of pollen, nectar, and nesting sites to be provided by their environment in order to survive, and if their environment is being disturbed or destroyed, some of their previously supplied resources may be in limited amounts (Steffan-Dewenter, Ingolf and Teja, Tscharntke. 2002).  Oftentimes, a generalist can swoop in and take over for the previous pollinator, but new pollinators may not be as effective (Kwak et al. 1998). If the insect or animal is not a generalist species, then it will have two choices: the pollinator can look for a new species of plant to feed from, or it can die off.

LOSS OF PLANT DIVERSITY
Pollinators are important drivers of diversity in the ecosystem by providing a mutualistic relationship to crops and wild plants all around the globe (Potts et al. 2010). Two out of eight papers noted, roughly 80% of all flowering plants reproduce with the help of an animal pollinator. So naturally, in a fragmented habitat, the loss of plants and plant diversity can lead to a major change in pollinator abundance and diversity. Lots of insects are tied to specific plants, for instance the monarch butterfly and milkweed plants. Monarchs use these plants to feed on in order to grow. If there is no milkweed, there is no monarch. These interactions are important to take note of because the effects can impact all humans on many levels. We depend on plants as a source of oxygen, for nutrients, to feed animals that we eventually eat,  and we also depend on plants for recreational purposes. I mean, what would the back porch of a cabin be without a full forest to drink your morning coffee to?

Four of the eight sources explicitly note that more research needs to be done on the topic of plant-pollinator interactions specifically in disturbed habitats. Much of the literature shows that both variables are affected, but a lot of the results are varied and it is also possible that some of the results are due to abiotic factors inhibiting plant growth.

TAKEAWAYS
The major takeaways that I got from my research is that: 1. we should do our best to preserve the natural land that we still have and come up with plans to help communities impacted by fragmentation, 2. more experiments need to be conducted on plant-pollinator interactions in these disturbed environments, and 3. we should take a pledge to elect Oprah as president in 2040.



WORKS CITED

Didham, Raphael K., Jaboury Ghazoul, Nigel E. Stork, and Andrew J. Davis. "Insects in fragmented forests: a functional approach." Trends in Ecology & Evolution 11.6 (1996): 255-60.

Ferreira, Patrícia Alves, Danilo Boscolo, and Blandina Felipe Viana. "What do we know about the effects of landscape changes on plant–pollinator interaction networks?" Ecological Indicators 31 (2013): 35-40.

Kwak, Manja M., Odilia Velterop, and Jelte Van Andel. "Pollen and gene flow in fragmented habitats." Applied Vegetation Science 1.1 (1998): 37-54. JSTOR.

Lienert, J. 2004. Habitat fragmentation effects on fitness of plant populations – a review. Journal for Nature Conservation 12:53–72.
 
Potts, Simon G., Jacobus C. Biesmeijer, Claire Kremen, Peter Neumann, Oliver Schweiger, and William E. Kunin. "Global pollinator declines: trends, impacts and drivers." Trends in Ecology & Evolution 25.6 (2010): 345-53.  

Skogen, K. A., T. Jogesh, E. T. Hilpman, S. L. Todd, M. K. Rhodes, S. M. Still, and J. B. Fant. "Land-use change has no detectable effect on reproduction of a disturbance-adapted, hawkmoth-pollinated plant species." American Journal of Botany 103.11 (2016): 1950-963. 

Steffan-Dewenter, Ingolf, and Teja Tscharntke. "Insect communities and biotic interactions on fragmented calcareous grasslands—a mini review." Biological Conservation 104.3 (2002): 275-84.

Valdivia, Carlos. "Negative effects of forest fragmentation and proximity to edges on pollination and herbivory of Bomarea salsilla (Alstroemeriaceae)." Plant Ecology and Evolution 144.3 (2011): 281-87. 


Picture: https://abinashpadhi.wordpress.com/2011/06/30/butterflies-in-hobbs-state-park-arkansas/