Seasonal litter contribution to total peat respiration from drained tropical peat under mature oil palm plantation

The amount of CO2 gas emissions in drained peatland for oil palm cultivation has been widely reported. However, the research addressing the contribution of litter respiration to peat and total respiration and its relationship with several environmental factors is found rare. The aim of this study was to measure peat and heterogeneous litter respiration of drained tropical peat in one year at a distance of 2.25 m and 4.50 m from mature oil palm trees of 14 years using the chamber method (Licor Li-830). In addition to CO2 efflux, we measured other environmental parameters, including peat temperature (10 cm depth), air temperature, groundwater table (GWL), and rainfall. Results showed that the mean total peat respiration (Rt) was 12.06 g CO2 m-2day-1, which consisted of 68% (8.24 g CO2 m-2day-1) peat (Rp) and root (Rr) respiration and 32% (3.84 g CO2 m-2day-1) of litter respiration (Rl) at the distance of 2.25 m from the palm tree. Meanwhile, at a farther distance, the Rt was 12.49 g CO2m-2day-1, the contribution of Rp was 56% (6.78 g CO2 m-2day-1), and Rl was higher than the closest distance (46%; 5.71 g CO2 m-2day-1). Thus, one-year observation resulting the mean Rt and Rr was 0.07–0.08 Mg CO2 ha-1 day-1, while Rl was 0.04–0.06 Mg CO2 ha-1 day-1. The means of Rt, Rp, and Rl were significantly different in the dry season than those recorded in the rainy season. The climatic-related variable such as peat and air temperature were chiefly governing respiration in peat under mature oil palm plantation, whereas the importance of other variables present at particular conditions. This paper provides valuable information concerning respiration in peat, especially for litter contribution and its relationship with environmental factors in peatland, contributing to global CO2 emission.

Decoupling litter respiration from whole-soil respiration along an elevation gradient in a Rocky Mountain mixed-conifer forest

Litter respiration (RL) represents a significant portion of whole-soil respiration (RS) in forests, yet climatic correlations with RL have seldom been examined. Because RL is reduced at low humidities and RS is reduced at low temperatures, these components may show divergent trends with elevation in western North American forests. Using a litter-removal experiment along a forested 750 m elevation gradient in the Rocky Mountains of northern Idaho, USA, we measured RS on soils from which litter had been removed (RNL) and, by difference, RL. Mean RL represented 16% (SE = 2%) of mean RS from July through October of 2007 and 2008. RS was highest at warmer times and sites, and was not suppressed by low soil moisture. In contrast, RL was highest at cooler times, when humidity and gravimetric litter water content were highest. RL was highest at mid-elevations, representing neither the warmest nor wettest sites. Sixty-three percent of variability in site RL was explained by both mean annual temperature (MAT) and mean annual relative humidity (MARH), including a positive interaction effect between MAT and MARH. Our results imply that the equilibration of litter with atmospheric humidity is an important control over litter respiration rates.

Characteristics of Soil Respiration in a Phyllostachys Pubescens Plantation in the Northeast of Subtropics

Soil respiration was continuously measured in situ by using Licor-8150 in aPhyllostachys pubescensplantation, located in Miaoshanwu Forest Ecosystem Research Station in Fuyang, Zhejiang Province. Soil respiration showed an obvious variation in season, which is consistent with the variation of soil temperature, peaking at the hottest month (August) and bottoming out at the coldest month (January). Moreover, the ratios of different soil respiration components to total soil respiration were different, with 25.7% in root respiration, 57.0% in litter respiration and 17.3% in heterotrophic respiration.

Decreased carbon limitation of litter respiration in a mortality-affected piñon–juniper woodland

Microbial respiration depends on microclimatic variables and carbon (C) substrate availability, all of which are altered when ecosystems experience major disturbance. Widespread tree mortality, currently affecting piñon–juniper ecosystems in southwestern North America, may affect C substrate availability in several ways, for example, via litterfall pulses and loss of root exudation. To determine piñon mortality effects on C and water limitation of microbial respiration, we applied field amendments (sucrose and water) to two piñon–juniper sites in central New Mexico, USA: one with a recent (< 1 yr), experimentally induced mortality event and a nearby site with live canopy. We monitored the respiration response to water and sucrose applications to the litter surface and to the underlying mineral soil surface, testing the following hypotheses: (1) soil respiration in a piñon–juniper woodland is water- and labile C-limited in both the litter layer and mineral soil; (2) piñon mortality reduces the C limitation of litter respiration; and (3) piñon mortality enhances the C limitation of mineral soil respiration. Litter respiration at both sites responded to increased water availability, yet surprisingly, mineral soil respiration was not limited by water. Consistent with hypothesis 2, C limitation of litter respiration was lower at the recent mortality site compared to the intact canopy site. Applications to the mineral soil showed evidence of reduction in CO2 flux on the girdled site and a non-significant increase on the control. We speculate that the reduction may have been driven by water-induced carbonate dissolution, which serves as a sink for CO2 and would reduce the net flux. Widespread piñon mortality may decrease labile C limitation of litter respiration, at least during the first growing season following mortality.

Influence of Long-Term Thinning on the Biomass Carbon and Soil Respiration in a Larch (Larix gmelinii) Forest in Northeastern China

Thinning management is used to improve timber production, but only a few data are available on how it influences ecosystem C sink capacity. This study aims to clarify the effects of thinning on C sinks of larch plantations, the most widespread forests in Northeastern China. Both C influx from biomass production and C efflux from each soil respiration component and its temperature sensitivity were determined for scaling-up ecosystem C sink estimation: microbial composition is measured for clarifying mechanism for respiratory changes from thinning treatment. Thinning management induced 6.23 mol C m−2 yr−1increase in biomass C, while the decrease in heterotrophic respiration (Rh) at the thinned sites (0.9 mol C m−2 yr−1) has enhanced 14% of this biomass C increase. This decrease inRhwas a sum of the 42% decrease (4.1 mol C m−2 yr−1) in litter respiration and 3.2 mol C m−2 yr−1more CO2efflux from mineral soil in thinned sites compared with unthinned control. Increases in temperature, temperature sensitivity, alteration of litters, and microbial composition may be responsible for the contrary changes inRhfrom mineral soil and litter respiration, respectively. These findings manifested that thinning management of larch plantations could enhance biomass accumulation and decrease respiratory efflux from soil, which resulted in the effectiveness improvement in sequestrating C in forest ecosystems.

Decreased carbon limitation of litter respiration in a mortality-affected piñon-juniper woodland

Microbial respiration depends on microclimatic variables and carbon (C) substrate availability, all of which are altered when ecosystems experience major disturbance. Widespread tree mortality, currently affecting piñon-juniper ecosystems in Southwestern North America, may affect C substrate availability in several ways; for example, via litterfall pulses and loss of root exudation. To determine piñon mortality effects on C and water limitation of microbial respiration, we applied field amendments (sucrose and water) to two piñon-juniper sites in central New Mexico, USA: one with a recent (< 1 yr), experimentally-induced mortality event and a nearby site with live canopy. We monitored the respiration response to water and sucrose applications to the litter surface and to the underlying mineral soil surface, testing the following hypotheses: (1) soil respiration in a piñon-juniper woodland is water- and labile C-limited in both the litter layer and mineral soil; (2) water and sucrose applications increase temperature sensitivity of respiration; (3) the mortality-affected site will show a reduction in C limitation in the litter; (4) the mortality-affected site will show an enhancement of C limitation in the mineral soil. Litter respiration at both sites responded to increased water availability, yet surprisingly, mineral soil respiration was not limited by water. Temperature sensitivity was enhanced by some of the sucrose and water treatments. Consistent with hypothesis 3, C limitation of litter respiration was lower at the recent mortality site compared to the intact canopy site. Results following applications to the mineral soil suggest the presence of abiotic effects of increasing water availability, precluding our ability to measure labile C limitation in soil. Widespread piñon mortality may decrease labile C limitation of litter respiration, at least during the first growing season following mortality.