Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.

[1] Deforestation and climate change have the capacity to alter rainfall regimes, water availability, and surface-atmosphere flux of water and energy of tropical forests, especially in ecotonal, semi-deciduous tropical forests of the southern Amazon Basin, which have experienced rapid regional warming and deforestation over the last three decades. To reduce uncertainty regarding current and future energy and water flux, micrometeorological measurements of latent (Q e ) and sensible heat flux (Q h ) and canopy conductance (G c ) were combined with measurements of sap flux density (F d ) and maximum leaf conductance (g smax ) to characterize the seasonal controls on mass (H 2 O) and energy exchange of an ecotonal, semi-deciduous forest in northern Mato Grosso, Brazil over the 2005-2006 annual cycle. Average diel patterns and daily rates of energy flux and conductance declined during the dry season; however, the decline in F d and Q e was smaller and/or more gradual than G c and g smax . Weekly averages of transpiration calculated from sap flow measurements during the dry-wet season transition period were positively correlated (r 2 = 0.47; p < 0.05; n = 11) with estimates of leaf area index (LAI) derived from the Modis-Aqua satellite platform while estimates of evapotranspiration ET derived from eddy covariance were not, presumably because these estimates also include an evaporation component. Overall, our results suggest that access to deep water reserves can support high rates of F d and Q e during the dry season, but because of high evaporative demand, declines in plant water potential lead to a corresponding decline in G c . Furthermore, seasonal variations in LAI, that are likely to be controlled in part by plant water status and phenology, constrain tree and stand transpiration. Thus the consistency of Q e over the annual cycle appears to be the result of trade-offs between water availability (rainfall, soil moisture, water potential), canopy structural properties (LAI), and meteorological conditions including vapor pressure deficit and net radiation.

The Pantanal is a biodiversity hotspot comprised of a mosaic of landforms that differ in vegetative assemblages and flooding dynamics. Tree islands provide refuge for terrestrial fauna during the flooding period and are particularly important to the regional ecosystem structure. Little soil CO2 research has been conducted in this region. We evaluated soil CO2 dynamics in relation to primary controlling environmental parameters (soil temperature and soil water). Soil respiration was computed using the gradient method using in situ infrared gas analyzers to directly measure CO2 concentration within the soil profile. Due to the cost of the sensors and associated equipment, this study was unreplicated. Rather, we focus on the temporal relationships between soil CO2 efflux and related environmental parameters. Soil CO2 efflux during the study averaged 3.53 µmol CO2 m−2 s−1, and was equivalent to an annual soil respiration of 1220 g C m−2 y−1. This efflux value, integrated over a year, is comparable to soil C stocks for 0–20 cm. Soil water potential was the measured parameter most strongly associated with soil CO2 concentrations, with high CO2 values observed only once soil water potential at the 10 cm depth approached zero. This relationship was exhibited across a spectrum of timescales and was found to be significant at a daily timescale across all seasons using conditional nonparametric spectral Granger causality analysis. Hydrology plays a significant role in controlling CO2 efflux from the tree island soil, with soil CO2 dynamics differing by wetting mechanism. During the wet-up period, direct precipitation infiltrates soil from above and results in pulses of CO2 efflux from soil. The annual flood arrives later, and saturates soil from below. While CO2 concentrations in soil grew very high under both wetting mechanisms, the change in soil CO2 efflux was only significant when soils were wet from above.

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Variations in Stand Structure and Diversity along a Soil Fertility Gradient in a Brazilian Savanna (Cerrado) in Southern Mato Grosso Forest, Range & Wildland Soils B razilian savanna, locally known as cerrado, covers approximately 20 to 25% of the total land cover of Brazil and is the second largest vegetation type following Amazonian forest (Furley and Ratter, 1988). Cerrado is composed of distinctive physiognomies that vary as a function of height, cover, and/ or density of trees (Goodland, 1971; Eiten, 1972; Furley and Ratter, 1988). The factors that affect the physiognomy and distribution of cerrado remain a subject of debate; however, seasonal variation in rainfall, soil fertility and drainage, and fire are considered the most important (Eiten, 1972; Furley and Ratter, 1988; Lopes and Cox, 1977). In terms of soil properties, variations in soil texture, water holding capacity, and chemical properties, such as pH and Al 3+ concentration, have been found to be important variables affecting cerrado physiognomy and tree species distribution (Lopes and Cox, 1977; Furley and Ratter, 1988; de Souza et al., 2007; de Assis et al., 2011). Nutrient limitation has been implicated as a primary factor inhibiting the development of forests in tropical savanna, and across large-scale fertility gradients, an increase in soil fertility can lead to an increase in the production of woody vegetation, and the density and cover of trees (Goodland and Pollard, 1973; Lopes

[1] Measurements of soil CO 2 efflux, litter production, and the surface litter pool biomass were made over a 1 year period in a tropical transitional forest near Sinop, Mato Grosso, Brazil with the aim of quantifying the seasonal variation in soil respiration and litter decomposition and the annual contribution of litter decomposition to soil CO 2 efflux. Average annual soil CO 2 efflux (±95% confidence interval (CI)) was 7.91 ± 1.16 g C m À2 d À1 . Soil CO 2 efflux was highest during the November-February wet season (9.15 ± 0.90 g C m À2 d À1 ) and lowest during the May-September dry season (6.19 ± 1.40 g C m À2 d À1 ), and over 60% of the variation in seasonal soil CO 2 efflux was explained by seasonal variations in soil temperature and moisture. Mass balance estimates of mean (±95% CI) decomposition rates were statistically different between the wet and dry seasons (0.66 ± 0.08 and 1.65 ± 0.10 g C m À2 d À1 , respectively), and overall, decomposition of leaf litter comprised 16% of the average annual soil respiration. Leaf litter production was higher during the dry season, and mean (±95% CI) leaf litter fall (5.6 ± 1.7 Mg ha À1