The Nutrient Status of Plant Roots Reveals Competition Intensities in Rubber Agroforestry Systems

Junen Wu,Chunfeng Chen,Pingyuan Wang,Zhixiang Wu,Fan Zhao,Wenjie Liu,Xiai Zhu,Huanhuan Zeng,Xiaojin Jiang

doi:10.3390/f11111163

Abstract

Controversial competition theories may confuse the current understanding of belowground plant competition and thus result in incorrect diagnoses and mitigation strategies for nutrient competition. As such, the management of nutrient competition is a major challenge in the application and development of rubber agroforestry systems (AFSs). To explore the effects of plant competition on the nutrient status of rubber AFSs, this study measured the carbon, nitrogen, and phosphorus concentrations of the litter and soil and in plant leaves, stems, and roots from five rubber plantations (i.e., rubber monocultures and rubber mixed with cocoa, coffee, tea, and Flemingia macrophylla (Willd.) Merr., 1910)). The relative competition intensity indexes were calculated to evaluate the competition intensity of each mixed-species system, and Bayesian networks were established to investigate the linkage effects of interspecific competition for nutrients. This study demonstrated that rubber trees had weak competition with cocoa trees, moderate competition with F. macrophylla and tea trees, and intense competition with coffee trees. With the increase in competition intensity, the negative effects of interspecific competition on soil gradually offset the improvement in soil nutrients achieved with intercropping. Nitrogen and phosphorous translocation from the stems to the roots was enhanced by competition. However, enhanced nutrient allocation to roots may have led to insufficient nitrogen and phosphorous supplies in plant leaves. The quality of the litter therefore decreased because the nutrient status of fallen leaves determines the initial litter conditions. Such consequences may reduce the release of nutrients from the litter to the soil and thus increase soil nutrient depletion. This study revealed that competition effects were most obvious for the root nutrient status, followed by the stem and leaf nutrient statuses. Moreover, this study further demonstrated that the nutrient concentration of plant roots can better indicate the intensity of nutrient competition than the nutrient concentration of other plant organs.

Highlights

IntroductionUnderstanding plantcompetition competition reveal how various plantmaintain species their maintain theirUnderstanding plant can can reveal how various plant species coexistence coexistence in natural [1] the anddesign help guide the designofand management of [2,3].artificial in natural ecosystems [1]ecosystems and help guide and management artificial ecosystemsThe ecosystems [2,3].hasThe latter advantage has more example, practical in significance—for in the latter advantage more practical significance—for the constructionexample, of rubber-based construction of rubber-based agroforestry1a)
This study addressed two scientific questions: (1) how does interspecific competition affect the nutrient status of each part of a rubber agroforestry system (AFS); (2) which link of nutrient cycling best reflects the intensity of interspecific competition in rubber AFSs? To address these questions, the nutrient competition intensity of each AFS was determined through a nutrient diagnosis of the entire system
The negative relative competition intensity (NRCI) indexes were lower in the rubber and coffee AFS (Figure 2), which means that the interspecific competition was more intense in this AFS

Summary

Introduction

IntroductionUnderstanding plantcompetition competition reveal how various plantmaintain species their maintain theirUnderstanding plant can can reveal how various plant species coexistence coexistence in natural [1] the anddesign help guide the designofand management of [2,3].artificial in natural ecosystems [1]ecosystems and help guide and management artificial ecosystemsThe ecosystems [2,3].hasThe latter advantage has more example, practical in significance—for in the latter advantage more practical significance—for the constructionexample, of rubber-based construction of rubber-based agroforestry1a). Understanding plant can can reveal how various plant species coexistence coexistence in natural [1] the anddesign help guide the designofand management of [2,3]. Artificial in natural ecosystems [1]ecosystems and help guide and management artificial ecosystems. The ecosystems [2,3].has. The latter advantage has more example, practical in significance—for in the latter advantage more practical significance—for the constructionexample, of rubber-based construction of rubber-based agroforestry. Suchsystems artificial(AFSs; forestsFigure could solve the disadvantages of rubber solve the disadvantages ofarubber monocultures and provide a series benefits to rubber monocultures and provide series of benefits to rubber cultivation areasof [4]; rubbercultivation. AFSs have been labeled asahaving a high economic potential and a high been labeled as having a high economic potential and high biodiversity and being environmentally biodiversity and being environmentally friendly and useful sustainable development many friendly and useful in sustainable development in many studiesin[2,4].

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