Can short-term pasture management increase C balance in the Atlantic Rainforest?

Few studies have shown the importance of different pasture management practices on C storage and the reduction of CO₂-C emissions in tropical conditions. The objective of the present study was to determine short-term changes in C pools and C balance from different pasture management practices established in the Atlantic Rainforest. A field study was carried out in Alegre, ES, Brazil from September 2013 to August 2014 to investigate the first-year effect of pasture management practices on a Udult clayey soil. The different pasture management practices studied included the following: control (CON), chiseled (CHI), fertilized (FER), burned (BUR), integrated with crop-livestock (iCL) systems, and plowed and harrowed (PH). Monthly disturbed and undisturbed soil samples were taken at two different layers (0.00-0.05 and 0.05-0.20 m) for chemical, physical, and organic matter characterization. C inputs monitored in aboveground pools included plant aerial parts and litter, and belowground pools included roots and soil C stocks. C outputs monitored were CO₂-C emissions, erosion water, and sediment. C balance was considered the difference between inputs and outputs in each treatment during four seasons. The spring and summer seasons had a strong influence on C inputs and outputs where there is significant difference between spring and summer, while the autumn and winter seasons had less influence. All pasture management practices exhibited positive C balance after 1 year. High values of C balance were verified in pastures fertilized (FER) (53.04 Mg ha^-1 year^-1. Intermediate C balance was found in the burned (BUR) (40.84 Mg ha^-1 year^-1), traditional control (CON) (40.31 Mg ha^-1 year^-1), and in the plowing and harrowing (PH) (40.02 Mg ha^-1 year^-1) management practices. The practices of chiseled (40.00 Mg ha^-1 year^-1) and integrated crop-livestock systems (iCL) (59.06 Mg ha^-1 year^-1) resulted in low C balance.

Understanding the Terrestrial Carbon Cycle: An Ecohydrological Perspective

The terrestrial carbon (C) cycle has a great role in influencing the climate with complex interactions that are spatially and temporally variable and scale-related. Hence, it is essential that we fully understand the scale-specific complexities of the terrestrial C-cycle towards (1) strategic design of monitoring and experimental initiatives and (2) also developing conceptualizations for modeling purposes. These complexities arise due to the nonlinear interactions of various components that govern the fluxes of mass and energy across the soil-plant-atmospheric continuum. Considering the critical role played by hydrological processes in governing the biogeochemical and plant physiological processes, a coupled representation of these three components (collectively referred to as ecohydrological approach) is critical to explain the complexity in the terrestrial C-cycling processes. In this regard, we synthesize the research works conducted in this broad area and bring them to a common platform with an ecohydrological spirit. This could aid in the development of novel concepts of nonlinear ecohydrological interactions and thereby help reduce the current uncertainties in the terrestrial C-cycling process. The usefulness of spatially explicit and process-based ecohydrological models that have tight coupling between hydrological, ecophysiological, and biogeochemical processes is also discussed.

Understanding of coupled terrestrial carbon, nitrogen and water dynamics-an overview

Coupled terrestrial carbon (C), nitrogen (N) and hydrological processes play a crucial role in the climate system, providing both positive and negative feedbacks to climate change. In this review we summarize published research results to gain an increased understanding of the dynamics between vegetation and atmosphere processes. A variety of methods, including monitoring (e.g., eddy covariance flux tower, remote sensing, etc.) and modeling (i.e., ecosystem, hydrology and atmospheric inversion modeling) the terrestrial carbon and water budgeting, are evaluated and compared. We highlight two major research areas where additional research could be focused: (i) Conceptually, the hydrological and biogeochemical processes are closely linked, however, the coupling processes between terrestrial C, N and hydrological processes are far from well understood; and (ii) there are significant uncertainties in estimates of the components of the C balance, especially at landscape and regional scales. To address these two questions, a synthetic research framework is needed which includes both bottom-up and top-down approaches integrating scalable (footprint and ecosystem) models and a spatially nested hierarchy of observations which include multispectral remote sensing, inventories, existing regional clusters of eddy-covariance flux towers and CO(2) mixing ratio towers and chambers.

Changes in net ecosystem productivity of boreal black spruce stands in response to changes in temperature at diurnal and seasonal time scales

Net ecosystem productivity (NEP) of boreal coniferous forests is believed to rise with climate warming, thereby offsetting some of the rise in atmospheric CO(2) concentration (C(a)) by which warming is caused. However, the response of conifer NEP to warming may vary seasonally, with rises in spring and declines in summer. To gain more insight into this response, we compared changes in CO(2) exchange measured by eddy covariance and simulated by the ecosystem process model ecosys under rising mean annual air temperatures (T(a)) during 2004-2006 at black spruce stands in Saskatchewan, Manitoba and Quebec. Hourly net CO(2) uptake was found to rise with warming at T(a) < 15 degrees C and to decline with warming at T(a) > 20 degrees C. As mean annual T(a) rose from 2004 to 2006, increases in net CO(2) uptake with warming at lower T(a) were greater than declines with warming at higher T(a) so that annual gross primary productivity and hence NEP increased. Increases in net CO(2) uptake measured at lower T(a) were explained in the model by earlier recovery of photosynthetic capacity in spring, and by increases in carboxylation activity, using parameters for the Arrhenius temperature functions of key carboxylation processes derived from independent experiments. Declines in net CO(2) uptake measured at higher T(a) were explained in the model by sharp declines in mid-afternoon canopy stomatal conductance (g(c)) under higher vapor pressure deficits (D). These declines were modeled from a hydraulic constraint to water uptake imposed by low axial conductivity of conifer roots and boles that forced declines in canopy water potential (psi(c)), and hence in g(c) under higher D when equilibrating water uptake with transpiration. In a model sensitivity study, the contrasting responses of net CO(2) uptake to specified rises in T(a) caused annual NEP of black spruce in the model to rise with increases in T(a) of up to 6 degrees C, but to decline with further increases at mid-continental sites with lower precipitation. However, these contrasting responses to warming also indicate that rises in NEP with climate warming would depend on the seasonality (spring versus summer) as well as the magnitude of rises in T(a).