School of Geography & Environmental Sciences, Ulster University, Cromore Road, BT52 1SA, Coleraine, United Kingdom.
Department of Life Sciences, Imperial College, Silwood Park, Ascot, Berkshire, SL5 7PY, United Kingdom.
Ecol Appl. 2017 Oct;27(7):2001-2012. doi: 10.1002/eap.1585. Epub 2017 Aug 17.
The functioning of human-managed grassland ecosystems strongly depends on how common management practices will affect grassland "belowground compartment" including soil biogeochemistry and plant roots. Key questions remain about how animal grazing, liming (e.g., the addition of CaCO to soils), and nutrient fertilization might affect, in the long-term, soil nutrient cycling and multiple root traits. Here we focus on a mesotrophic grassland located in Berkshire, UK, where contrasting levels of rabbit grazing, liming, and different inorganic fertilizers have been applied since 1991. We ask how (1) soil nitrogen (N) availability and cycling, (2) total root mass, (3) root mass decomposition, and (4) arbuscular mycorrhizal fungal (AMF) root colonization might respond to 22 years of very different management. We found that liming strongly affected total root mass, root decomposition, root AMF colonization as well as soil N availability and cycling and that these effects were mainly driven by liming-induced increases in soil pH. Increases in soil pH were associated with significant (1) decreases in root mass, (2) increases in root mass decomposability and in the mineralization of N in decomposing root detritus, and (3) increases in AMF infection. Soil pH was also significantly related to greater N availability (i.e., soil NO levels) and to lower δ N natural abundance, which suggests more efficient N uptake by plants in limed soils as we found in our study. The application of multiple nutrients (N, P, K, Mg) also reduced total root mass, while N-only fertilization was associated with greater AMF infection. Surprisingly the long-term impact of grazing was generally weak and not significant on most plant and soil parameters. Despite soil pH affecting most belowground variables, changes in soil pH were not associated with any change in soil C and N stocks. Because liming can improve nutrient cycling (and benefits soil pH and grass yields) without negatively affecting soil C sequestration, we suggest that regular liming applications may provide management solutions for increasing the long-term sustainability of permanent grassland.
人类管理的草原生态系统的功能在很大程度上取决于常见的管理实践将如何影响草原的“地下部分”，包括土壤生物地球化学和植物根系。关于动物放牧、石灰（例如，向土壤中添加 CaCO）和养分施肥如何在长期内影响土壤养分循环和多种根系特征，仍有一些关键问题尚未得到解答。在这里，我们关注的是位于英国伯克郡的一个中营养草原，自 1991 年以来，该草原采用了不同水平的兔放牧、石灰和不同的无机肥料。我们想知道：（1）土壤氮（N）的有效性和循环，（2）总根质量，（3）根质量分解，以及（4）丛枝菌根真菌（AMF）根定殖将如何对 22 年的不同管理做出响应。我们发现，石灰处理强烈影响总根质量、根分解、根 AMF 定殖以及土壤 N 的有效性和循环，这些影响主要是由石灰处理引起的土壤 pH 值升高所驱动的。土壤 pH 值的升高与以下几个方面呈显著负相关：（1）根质量的减少，（2）根质量分解率的增加，以及（3）N 在分解根碎屑中的矿化率的增加，以及（3）AMF 感染的增加。土壤 pH 值还与较高的 N 有效性（即土壤 NO 水平）和较低的δ N 自然丰度显著相关，这表明在石灰处理的土壤中，植物的 N 吸收效率更高，这也是我们在研究中发现的。多种养分（N、P、K、Mg）的施用也降低了总根质量，而仅 N 施肥与更高的 AMF 感染有关。令人惊讶的是，放牧的长期影响通常较弱，对大多数植物和土壤参数都没有显著影响。尽管土壤 pH 值影响了大多数地下变量，但土壤 pH 值的变化与土壤 C 和 N 储量的任何变化都没有关联。由于石灰处理可以改善养分循环（并有利于土壤 pH 值和草产量）而不会对土壤 C 固存产生负面影响，因此我们认为，定期石灰处理可能为提高永久性草地的长期可持续性提供管理解决方案。
