Using a Bottom-Up Approach to Scale Leaf Photosynthetic Traits of Oil Palm, Rubber, and Two Coexisting Tropical Woody Species

Ashehad A Ali,Robert Pangle,Bambang Irawan,Suria Tarigan,Marife D Corre,Edzo Veldkamp,Alexander Olchev,Alexander Knohl,Fabian Brambach,Fernando E Moyano,Andi Nur Cahyo,Tania June,Branindityo Nugroho,Rahmi Ariani,Emanuel Blei,Michael W Jenkins,Christian Stiegler

doi:10.3390/f12030359

Abstract

Rainforest conversion to woody croplands impacts the carbon cycle via ecophysiological processes such as photosynthesis and autotrophic respiration. Changes in the carbon cycle associated with land-use change can be estimated through Land Surface Models (LSMs). The accuracy of carbon flux estimation in carbon fluxes associated with land-use change has been attributed to uncertainties in the model parameters affecting photosynthetic activity, which is a function of both carboxylation capacity (Vcmax) and electron transport capacity (Jmax). In order to reduce such uncertainties for common tropical woody crops and trees, in this study we measured Vcmax25 (Vcmax standardized to 25 °C), Jmax25 (Jmax standardized to 25 °C) and light-saturated photosynthetic capacity (Amax) of Elaeis guineensis Jacq. (oil palm), Hevea brasiliensis (rubber tree), and two native tree species, Eusideroxylon zwageri and Alstonia scholaris, in a converted landscape in Jambi province (Sumatra, Indonesia) at smallholder plantations. We considered three plantations; a monoculture rubber, a monoculture oil palm, and an agroforestry system (jungle rubber plantation), where rubber trees coexist with some native trees. We performed measurements on leaves at the lower part of the canopy, and used a scaling method based on exponential function to scale up photosynthetic capacity related traits to the top of the canopy. At the lower part of the canopy, we found (i) high Vcmax25 values for H. brasiliensis from monoculture rubber plantation and jungle rubber plantation that was linked to a high area-based leaf nitrogen content, and (ii) low value of Amax for E. guineensis from oil palm plantation that was due to a low value of Vcmax25 and a high value of dark respiration. At the top of the canopy, Amax varied much more than Vcmax25 among different land-use types. We found that photosynthetic capacity declined fastest from the top to the lower part of the canopy in oil palm plantations. We demonstrate that photosynthetic capacity related traits measured at the lower part of the canopy can be successfully scaled up to the top of the canopy. We thus provide helpful new data that can be used to constrain LSMs that simulate land-use change related to rubber and oil palm expansion.

Highlights

Tropical forest conversions to different land use significantly impact water and carbon cycle dynamics by modifying carbon sequestration and carbon emission rates [1,2]
In order to reduce such uncertainties for common tropical woody crops and trees, in this study we measured Vcmax25 (Vcmax standardized to 25 ◦C), Jmax25 (Jmax standardized to 25 ◦C) and light-saturated photosynthetic capacity (Amax) of Elaeis guineensis Jacq., Hevea brasiliensis, and two native tree species, Eusideroxylon zwageri and Alstonia scholaris, in a converted landscape in Jambi province (Sumatra, Indonesia) at smallholder plantations
Land-use change (LUC) from native forest vegetation to rubber and oil palm plantations has increased the income of farmers of Jambi [4,6,7] while at the same time leading to significant ecological costs: decreases in above-ground and below-ground carbon stocks [8,9,10], reduction in soil nitrogen availability [11] and increases in soil N2O emissions following N fertilization [12]

Summary

Introduction

Tropical forest conversions to different land use significantly impact water and carbon cycle dynamics by modifying carbon sequestration and carbon emission rates [1,2]. Land-use change (LUC) from native forest vegetation to rubber and oil palm plantations has increased the income of farmers of Jambi [4,6,7] while at the same time leading to significant ecological costs: decreases in above-ground and below-ground carbon stocks [8,9,10], reduction in soil nitrogen availability [11] and increases in soil N2O emissions following N fertilization [12]. Despite their importance for biogeochemical cycles, the impacts of LUC in the tropics are not well represented in Land Surface Models (LSMs)

Objectives

Methods

Results

Discussion

Conclusion