Nitrogen and phosphorus availability alters tree-grass competition intensity in savannas
Nitrogen and phosphorus availability alters tree-grass competition intensity in savannas
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氮和磷的有效性改变了稀树草原的树草竞争强度
DOI：
10.1111/1365-2745.14284
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发表时间：
2024
影响因子：
5.5
通讯作者：
Biro A
中科院分区：
文献类型：
--
作者：
Biro A
氮 (N) 和磷 (P) 等植物必需大量营养素会限制稀树草原树木的生长，并且与降雨、火灾和食草一样，是稀树草原植被动态的重要决定因素。氮和磷如何影响树草竞争及其共存仍不清楚，这阻碍了我们预测稀树草原如何响应养分循环变化的能力。在这里，我们评估（1）树木和草对氮和磷可用性的反应是否不同，或（2）草在低营养环境中是否更具竞争力，而树木在高营养环境中是否更具竞争力。为此，我们在完全因子养分和竞争处理（有/无竞争者、低/高氮供应率和低/高磷供应率）下种植来自南非克鲁格国家公园的 6 种树和 1 种草的树苗，时间为 16 周，浇水方式旨在模拟中性稀树草原的雨季降雨。树木和草最积极地寻找氮，并根据氮的可用性不同地分配生物量。总体而言，树木在与草的竞争中生长速度下降，即使在树木生长速度更快的高营养环境中也是如此。草始终是更好的地下竞争者，利用积极的营养物觅食策略，包括响应氮的高根磷酸酶活性和大根生物量分配。合成。在低营养环境中（例如营养贫乏的沙质土壤），营养物质可能会限制树木生长。营养丰富的环境有利于树木生长，但草继续与树木进行有效竞争。了解这对于生态系统对养分可用性的反应意味着什么并非易事，特别是在火灾和食草动物的背景下。然而，很明显，土壤养分可能会影响稀树草原中的树木和草的生长和竞争，这表明未来养分循环的变化，例如氮沉降，可能对稀树草原植被产生重要影响。
Plant essential macronutrients like nitrogen (N) and phosphorus (P) can limit savanna tree growth and are important determinants of savanna vegetation dynamics, along with rainfall, fire and herbivory. How nitrogen and phosphorus shape tree‐grass competition and their coexistence remain unclear, hindering our ability to predict how savannas may respond to altered nutrient cycling.Here, we evaluate (1) if trees and grasses respond differently to N versus P availability, or (2) if grasses are more competitive in low nutrient environments while trees are more competitive in high nutrient environments. To do this, we grew saplings of 6 tree and 1 grass species from the Kruger National Park, South Africa, for 16 weeks under fully factorial nutrient and competition treatments (with/without competitors, low/high rate of N supply and low/high rate of P supply) under a watering regime designed to mimic wet season rainfall in a mesic savanna.Trees and grasses foraged most aggressively for nitrogen and allocated biomass differently depending on nitrogen availability. Overall, tree growth decreased in competition with grass, even in high nutrient environments where they grew faster. Grasses were always better below‐ground competitors, utilising aggressive nutrient foraging strategies, including high root phosphatase activity in response to nitrogen and large root biomass allocation.Synthesis. In low nutrient environments (e.g. on nutrient‐poor sandy soils), nutrients may limit tree growth. Nutrient rich environments enable tree growth, but grasses continue to compete effectively with trees. Understanding what this means for ecosystem responses to nutrient availability is not trivial, especially in the context of fire and herbivory. However, it is clear that soil nutrients likely affect tree and grass growth and competition in savannas, which suggests that future changes in nutrient cycling, such as N deposition, may have important effects on savanna vegetation.