Effects of shading on the growth and leaf photosynthetic characteristics of three forages in an apple orchard on the Loess Plateau of eastern Gansu, China.

Mei Yang,Minguo Liu,Jiaoyun Lu,Huimin Yang

doi:10.7717/peerj.7594

Abstract

BackgroundInclusion of forage into the orchard is of great help in promoting the use efficiency of resources, while shading from trees restricts forage growth and production in the Loess Plateau of China. This study was aimed to investigate how tree shading affected leaf trait, photosynthetic gas exchange and chlorophyll feature of forages under the tree in the orchard-forage system.MethodsThe shading treatments were set as partially cutting branches (reduced shading), normal fruit tree shading (normal shading) and normal tree shading plus sun-shading net (enhanced shading) in an apple orchard. Leaf trait, photosynthesis, chlorophyll component and fluorescence related parameters were measured with lucerne (Medicago sativa), white clover (Trifolium repens) and cocksfoot (Dactylis glomerata) which were sown under apple trees.ResultsShading imposed significant impacts on the growth and leaf photosynthetic characteristics, while there were differences among species. Enhanced shading decreased leaf thickness, leaf dry matter content (LDMC) and leaf mass per unit area (LMA). Biomass accumulation decreased with enhanced shading in cocksfoot, but did not change in white clover and lucerne which had much lower biomass accumulation than cocksfoot. Enhanced shading reduced net photosynthetic rate (Pn) of white clover and lucerne, but rarely affected cocksfoot, while it decreased instantaneous water use efficiency (WUEi) of cocksfoot but had few effects on the other forages. Enhanced shading reduced leaf dark respiration rate (Rd), light compensation point (LCP) and maximum assimilation rate. The Rd and LCP of cocksfoot were much lower than those of white clover and lucerne. Chlorophyll contents and chlorophyll a/b changed little with shading. Cocksfoot had the highest contents but lowest ratio. Maximum photochemical rate of photosystem II increased and non-photochemical quenching decreased with enhanced shading in cocksfoot, while did not change in the other forages.DiscussionLeaf trait, photosynthetic gas exchange and chlorophyll feature were variously affected by species, shading and their interaction. Cocksfoot was more efficient than the other two forages in use of weakened light and more tolerant to tree shading. In the apple orchard, we recommend that reducing the density of apple tree or partially cutting branches together with selecting some shading-tolerant forages, i.e., cocksfoot, would be a practical option for the orchard-forage system in the Loess Plateau of China.

Highlights

Traditional orchard performance with bare ground or simple tillage to the soil has led to serious soil erosion and low use efficiency of resources, such as light, soil water and nutrients (Shui et al, 2008)
The experiment was conducted in a 7 year–old apple orchard at Qingyang Loess Plateau Pastoral Agriculture Station of Lanzhou University (35◦40 N, 107◦51 E), which locates in Qingyang, eastern Gansu of China with a typical continental climate
The leaf dry matter content (LDMC) and leaf mass per unit area (LMA) of three forages were affected by shading, species and their interaction, while the leaf thickness (LT) was only affected by shading and the biomass was only affected by species (Table 1)

Summary

Introduction

Traditional orchard performance with bare ground or simple tillage to the soil has led to serious soil erosion and low use efficiency of resources, such as light, soil water and nutrients (Shui et al, 2008). Sowing grass may potentially adjust the enrichment and paucity of soil water content to keep it relatively stable (Liu et al, 2013) It can reduce surface runoff and enhance infiltration, alleviating soil erosion (Fourie, Louw & Agenbag, 2007). Soil microbial diversity and activity increase in the orchard after sowing grass (Whitelaw-Weckert et al, 2007), which may be helpful for the decomposition of soil organism humus (Wardle et al, 2001) Under this system the competition for soil nutrient is relatively subtle due to the improvement of soil fertility by grasses and artificial fertilization. Enhanced shading reduced net photosynthetic rate (Pn) of white clover and lucerne, but rarely affected cocksfoot, while it decreased instantaneous water use efficiency (WUEi) of cocksfoot but had few effects on the other forages. We recommend that reducing the density of apple tree or partially cutting branches together with selecting some shading-tolerant forages, i.e., cocksfoot, would be a practical option for the orchard-forage system in the Loess Plateau of China

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