Pierre Suzanne, Litton Creighton M, Giardina Christian P, Sparks Jed P, Fahey Timothy J
Department of Ecology and Evolutionary Biology Cornell University Ithaca New York USA.
Department of Integrative Biology University of California, Berkeley Berkeley California USA.
Ecol Evol. 2020 Aug 28;10(18):9635-9646. doi: 10.1002/ece3.6561. eCollection 2020 Sep.
Mean annual temperature (MAT) is an influential climate factor affecting the bioavailability of growth-limiting nutrients nitrogen (N) and phosphorus (P). In tropical montane wet forests, warmer MAT drives higher N bioavailability, while patterns of P availability are inconsistent across MAT. Two important nutrient acquisition strategies, fine root proliferation into bulk soil and root association with arbuscular mycorrhizal fungi, are dependent on C availability to the plant via primary production. The case study presented here tests whether variation in bulk soil N bioavailability across a tropical montane wet forest elevation gradient (5.2°C MAT range) influences (a) morphology fine root proliferation into soil patches with elevated N, P, and N+P relative to background soil and (b) arbuscular mycorrhizal fungal (AMF) colonization of fine roots in patches. We created a fully factorial fertilized root ingrowth core design (N, P, N+P, unfertilized control) representing soil patches with elevated N and P bioavailability relative to background bulk soil. Our results show that percent AMF colonization of roots increased with MAT ( = .19, = .004), but did not respond to fertilization treatments. Fine root length (FRL), a proxy for root foraging, increased with MAT in N+P-fertilized patches only ( = .02), while other fine root morphological parameters did not respond to the gradient or fertilized patches. We conclude that in N-rich, fine root elongation into areas with elevated N and P declines while AMF abundance increases with MAT. These results indicate a tradeoff between P acquisition strategies occurring with changing N bioavailability, which may be influenced by higher C availability with warmer MAT.
年平均温度（MAT）是一个有影响力的气候因素，会影响生长限制养分氮（N）和磷（P）的生物有效性。在热带山地湿润森林中，较高的MAT会提高N的生物有效性，而P的有效性模式在不同的MAT条件下并不一致。两种重要的养分获取策略，即细根向大体积土壤中的增殖以及根与丛枝菌根真菌的共生，都依赖于植物通过初级生产获得的碳。本文呈现的案例研究检验了热带山地湿润森林海拔梯度（MAT范围为5.2°C）上大体积土壤中N生物有效性的变化是否会影响：（a）相对于背景土壤，细根向N、P和N+P含量升高的土壤斑块中的增殖形态；（b）斑块中细根的丛枝菌根真菌（AMF）定殖情况。我们创建了一个完全析因施肥的根系生长核心设计（N、P、N+P、未施肥对照），以代表相对于背景大体积土壤而言N和P生物有效性升高的土壤斑块。我们的结果表明，根的AMF定殖百分比随MAT升高而增加（r = 0.19，P = 0.004），但对施肥处理没有响应。细根长度（FRL）作为根系觅食的一个指标，仅在N+P施肥的斑块中随MAT升高而增加（P = 0.02），而其他细根形态参数对该梯度或施肥斑块没有响应。我们得出结论，在富含N的情况下，细根向N和P含量升高区域的伸长会减少，而AMF丰度随MAT升高而增加。这些结果表明，随着N生物有效性的变化，P获取策略之间存在权衡，这可能受到MAT升高时更高的碳有效性的影响。
