Primary Production In Tropical Forests Research Articles

Drought drives rapid shifts in tropical rainforest soil biogeochemistry and greenhouse gas emissions

Climate change models predict more frequent and severe droughts in the humid tropics. How drought will impact tropical forest carbon and greenhouse gas dynamics is poorly understood. Here we report the effects of the severe 2015 Caribbean drought on soil moisture, oxygen, phosphorus (P), and greenhouse gas emissions in a humid tropical forest in Puerto Rico. Drought significantly decreases inorganic P concentrations, an element commonly limiting to net primary productivity in tropical forests, and significantly increases organic P. High-frequency greenhouse gas measurements show varied impacts across topography. Soil carbon dioxide emissions increase by 60% on slopes and 163% in valleys. Methane (CH4) consumption increases significantly during drought, but high CH4 fluxes post-drought offset this sink after 7 weeks. The rapid response and slow recovery to drought suggest tropical forest biogeochemistry is more sensitive to climate change than previously believed, with potentially large direct and indirect consequences for regional and global carbon cycles.

Pervasive phosphorus limitation of tree species but not communities in tropical forests.

Phosphorus availability is widely assumed to limit primary productivity in tropical forests, but support for this paradigm is equivocal. Although biogeochemical theory predicts that phosphorus limitation should be prevalent on old, strongly weathered soils, experimental manipulations have failed to detect a consistent response to phosphorus addition in species-rich lowland tropical forests. Here we show, by quantifying the growth of 541 tropical tree species across a steep natural phosphorus gradient in Panama, that phosphorus limitation is widespread at the level of individual species and strengthens markedly below a threshold of two parts per million exchangeable soil phosphate. However, this pervasive species-specific phosphorus limitation does not translate into a community-wide response, because some species grow rapidly on infertile soils despite extremely low phosphorus availability. These results redefine our understanding of nutrient limitation in diverse plant communities and have important implications for attempts to predict the response of tropical forests to environmental change.

不同林龄橡胶(Hevea brasiliensis)林土壤微生物群落和磷组分的变化

PDF HTML阅读 XML下载 导出引用 引用提醒 不同林龄橡胶(Hevea brasiliensis)林土壤微生物群落和磷组分的变化 DOI: 10.5846/stxb201705020803 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31640014）；中央级公益性科研院所基本科研业务费专项（17CXTD-04，2015hzs1J012）；海南省自然科学基金（317235） Effects of rubber (Hevea brasiliensis) plantations on soil phosphorus fractions and microbial community composition Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:橡胶林是我国热带地区重要的经济林，而土壤磷是热带地区植物生长的重要限制因子之一，理解土壤磷转化机理对于生态系统的磷管理和可持续发展具有重要意义。因此，以热带地区海南儋州不同林龄（4、15、31a）橡胶人工林为研究对象，采用Hedley连续浸提法研究了土壤磷组分，磷脂脂肪酸法（Phospholipid fatty acids，PLFAs）分析了土壤微生物群落。结果表明，在橡胶林内各磷组分的相对含量大小顺序为：闭蓄态磷 > 中等活性态磷 > 活性态磷 > 团聚体内磷 > 钙磷。随着林龄的增加，橡胶林土壤中的磷组分发生显著变化。4、15、31a橡胶林的闭蓄态磷分别占总提取磷的52.61%、47.17%和34.91%，而活性态磷分别占总提取磷的6.67%、11.32%、13.68%。土壤总微生物、细菌、革兰氏阴性菌（G-）、革兰氏阳性菌（G+）的PLFAs含量均表现为15a > 4a > 31a，而31a橡胶林放线菌、真菌（F）和丛枝菌根真菌（AMF）的PLFAs含量均低于4a和15a。冗余分析（RDA）显示，全氮、有机碳、pH、F、AMF、G-、G+是引起不同林龄橡胶林土壤磷组分变化的重要贡献因子。研究表明，在橡胶林发育过程中，土壤理化性质和微生物群落发生了明显的变化，进而影响到土壤磷的转化过程。 Abstract:Phosphorus (P) is recognized as one of the most limiting nutrients for primary production in tropical forests because much of the soil P stocks are geochemically bound to iron and aluminum oxides in forms that are largely unavailable for plant uptake. The availability of P to microorganisms and plants can be assessed by evaluating different soil P fractions, and soil P occurs in both organic and inorganic forms, which differ in behavior, mobility, and bioavailability (i.e., labile P, moderately labile P, non-labile P). Labile and non-labile P fractions can serve as sources or sinks of available P, and non-labile P can be released into soil solutions as available P through desorption when the content of available P decreases in the soil. Therefore, it is critical to understand the transformation between different soil P fractions when developing best practices for fertilizer management that aim to enhance the P use efficiency of agricultural systems. Soil microorganisms are important mediators of P mineralization and immobilization, owing to their ability to reduce P availability by immobilizing P in their biomass, which subsequently increases stocks of microbial P in the soil. In addition, lower available P content was observed in tropical soil, accompanied by higher soil phosphatase activity. Furthermore, arbuscular mycorrhizal fungi (AMF) can take up P from pools that are normally considered unavailable to plants. However, the relationship between the dynamics of soil P forms, soil properties, and soil microbial communities has yet to be established in rubber plantation at different ages. Therefore, we compared the soil P fractions (i.e., labile P, moderately labile P, sonicate P, Ca-P, and occluded P) and soil microbial community composition of 4-, 15-, and 31-year-old rubber plantations on Hainan Island, Southern China. The aims of this study were (1) to determine whether the soil P stock and fractions would change with increasing plantation age; (2) to test whether the composition of soil microbial communities would change with plantation age; and (3) to quantify the relationships between P fraction, microbial community, and other soil attributes. The results could be used to develop recommended P fertilizer management practices for sustainable rubber plantations. We found that occluded P was the largest phosphorus fraction, followed by moderately labile P, labile P, sonicate P, and Ca-P in all plantations. The levels of bacteria and both gram-positive and gram-negative bacterial Phospholipid fatty acids (PLFAs) were highest in the 15-year-old plantation, whereas the levels of actinomycetes, arbuscular mycorrhizal fungi (16:1ω5c), and fungal PLFAs were lowest in the 31-year-old plantation. The level of soil acid phosphatase activity did not change with increasing plantation age, and redundancy analysis indicated that both biotic and abiotic factors were important contributors to variation in soil P fractions. Accordingly, the present study demonstrates that the age of rubber plantations significantly affects the soil physicochemical properties and microbial communities of rubber plantations and, consequently, soil P availability and cycling. 参考文献 相似文献 引证文献

Seasonal trends of Amazonian rainforest phenology, net primary productivity, and carbon allocation

AbstractThe seasonality of solar irradiance and precipitation may regulate seasonal variations in tropical forests carbon cycling. Controversy remains over their importance as drivers of seasonal dynamics of net primary productivity in tropical forests. We use ground data from nine lowland Amazonian forest plots collected over 3 years to quantify the monthly primary productivity (NPP) of leaves, reproductive material, woody material, and fine roots over an annual cycle. We distinguish between forests that do not experience substantial seasonal moisture stress (“humid sites”) and forests that experience a stronger dry season (“dry sites”). We find that forests from both precipitation regimes maximize leaf NPP over the drier season, with a peak in production in August at both humid (mean 0.39 ± 0.03 Mg C ha−1 month−1 in July, n = 4) and dry sites (mean 0.49 ± 0.03 Mg C ha−1 month−1 in September, n = 8). We identify two distinct seasonal carbon allocation patterns (the allocation of NPP to a specific organ such as wood leaves or fine roots divided by total NPP). The forests monitored in the present study show evidence of either (i) constant allocation to roots and a seasonal trade‐off between leaf and woody material or (ii) constant allocation to wood and a seasonal trade‐off between roots and leaves. Finally, we find strong evidence of synchronized flowering at the end of the dry season in both precipitation regimes. Flower production reaches a maximum of 0.047 ± 0.013 and 0.031 ± 0.004 Mg C ha−1 month−1 in November, in humid and dry sites, respectively. Fruitfall production was staggered throughout the year, probably reflecting the high variation in varying times to development and loss of fruit among species.

Short-term variability in labile soil phosphorus is positively related to soil moisture in a humid tropical forest in Puerto Rico

Primary productivity in tropical forests is often considered limited by phosphorus (P) availability. Microbial activity is a key regulator of available P through organic matter decomposition (supply) as well as microbial immobilization (depletion). Environmental conditions, such as soil moisture and temperature can fluctuate significantly on hourly to daily time-scales in tropical forested ecosystems. Given the ability of microbes to respond rapidly to changing environmental conditions we would expect concomitant changes in the available soil P pool. Despite the potential for soil P availability to vary on short time-scales, research that investigates hourly to daily changes in the available soil P pool in tropical forests is extremely rare. We quantified diurnal fluctuations in labile soil P and the importance of biotic and abiotic factors in driving these patterns in a wet tropical forest in Puerto Rico. Hourly measurements of Bray-extractable P were made from sunrise to sunset on five separate days along with measurements of soil temperature, moisture, pH, soil respiration, and solar radiation. While we found no significant diurnal variation in labile P, it did, however, vary significantly across the five sample days (2.8–3.8 µg/g). The day-to-day variation in labile P was positively related to soil moisture (R2 = 0.42, p = 0.009). These findings illustrate the potential for rapid change in the available P pool in response to variable soil moisture status as well as the importance of considering soil moisture conditions when estimating P availability in the humid tropics.

Fine-root responses to fertilization reveal multiple nutrient limitation in a lowland tropical forest.

Questions remain as to which soil nutrients limit primary production in tropical forests. Phosphorus (P) has long been considered the primary limiting element in lowland forests, but recent evidence demonstrates substantial heterogeneity in response to nutrient addition, highlighting a need to understand and diagnose nutrient limitation across diverse forests. Fine-root characteristics including their abundance, functional traits, and mycorrhizal symbionts can be highly responsive to changes in soil nutrients and may help to diagnose nutrient limitation. Here, we document the response of fine roots to long-term nitrogen (N), P, and potassium (K) fertilization in a lowland forest in Panama. Because this experiment has demonstrated that N and K together limit tree growth and P limits fine litter production, we hypothesized that fine roots would also respond to nutrient addition. Specifically we hypothesized that N, P, and K addition would reduce the biomass, diameter, tissue density, and mycorrhizal colonization of fine roots, and increase nutrient concentration in root tissue. Most morphological root traits responded to the single addition of K and the paired addition of N and P, with the greatest response to all three nutrients combined. The addition of N, P, and K together reduced fine-root biomass, length, and tissue density, and increased specific root length, whereas root diameter remained unchanged. Nitrogen addition did not alter root N concentration, but P and K addition increased root P and K concentration, respectively. Mycorrhizal colonization of fine roots declined with N, increased with P, and was unresponsive to K addition. Although plant species composition remains unchanged after 14 years of fertilization, fine-root characteristics responded to N, P, and K addition, providing some of the strongest stand-level responses in this experiment. Multiple soil nutrients regulate fine-root abundance, morphological and chemical traits, and their association with mycorrhizal fungi in a species-rich lowland tropical forest.

Amazon forests maintain consistent canopy structure and greenness during the dry season

The seasonality of sunlight and rainfall regulates net primary production in tropical forests. Previous studies have suggested that light is more limiting than water for tropical forest productivity, consistent with greening of Amazon forests during the dry season in satellite data. We evaluated four potential mechanisms for the seasonal green-up phenomenon, including increases in leaf area or leaf reflectance, using a sophisticated radiative transfer model and independent satellite observations from lidar and optical sensors. Here we show that the apparent green up of Amazon forests in optical remote sensing data resulted from seasonal changes in near-infrared reflectance, an artefact of variations in sun-sensor geometry. Correcting this bidirectional reflectance effect eliminated seasonal changes in surface reflectance, consistent with independent lidar observations and model simulations with unchanging canopy properties. The stability of Amazon forest structure and reflectance over seasonal timescales challenges the paradigm of light-limited net primary production in Amazon forests and enhanced forest growth during drought conditions. Correcting optical remote sensing data for artefacts of sun-sensor geometry is essential to isolate the response of global vegetation to seasonal and interannual climate variability.

The allocation of ecosystem net primary productivity in tropical forests

The allocation of the net primary productivity (NPP) of an ecosystem between canopy, woody tissue and fine roots is an important descriptor of the functioning of that ecosystem, and an important feature to correctly represent in terrestrial ecosystem models. Here, we collate and analyse a global dataset of NPP allocation in tropical forests, and compare this with the representation of NPP allocation in 13 terrestrial ecosystem models. On average, the data suggest an equal partitioning of allocation between all three main components (mean 34 ± 6% canopy, 39 ± 10% wood, 27 ± 11% fine roots), but there is substantial site-to-site variation in allocation to woody tissue versus allocation to fine roots. Allocation to canopy (leaves, flowers and fruit) shows much less variance. The mean allocation of the ecosystem models is close to the mean of the data, but the spread is much greater, with several models reporting allocation partitioning outside of the spread of the data. Where all main components of NPP cannot be measured, litterfall is a good predictor of overall NPP (r(2) = 0.83 for linear fit forced through origin), stem growth is a moderate predictor and fine root production a poor predictor. Across sites the major component of variation of allocation is a shifting allocation between wood and fine roots, with allocation to the canopy being a relatively invariant component of total NPP. This suggests the dominant allocation trade-off is a 'fine root versus wood' trade-off, as opposed to the expected 'root-shoot' trade-off; such a trade-off has recently been posited on theoretical grounds for old-growth forest stands. We conclude by discussing the systematic biases in estimates of allocation introduced by missing NPP components, including herbivory, large leaf litter and root exudates production. These biases have a moderate effect on overall carbon allocation estimates, but are smaller than the observed range in allocation values across sites.

Tropical rain forest tree growth and atmospheric carbon dynamics linked to interannual temperature variation during 1984-2000.

During 1984-2000, canopy tree growth in old-growth tropical rain forest at La Selva, Costa Rica, varied >2-fold among years. The trees' annual diameter increments in this 16-yr period were negatively correlated with annual means of daily minimum temperatures. The tree growth variations also negatively covaried with the net carbon exchange of the terrestrial tropics as a whole, as inferred from nearly pole-to-pole measurements of atmospheric carbon dioxide (CO(2)) interpreted by an inverse tracer-transport model. Strong reductions in tree growth and large inferred tropical releases of CO(2) to the atmosphere occurred during the record-hot 1997-1998 El Niño. These and other recent findings are consistent with decreased net primary production in tropical forests in the warmer years of the last two decades. As has been projected by recent process model studies, such a sensitivity of tropical forest productivity to on-going climate change would accelerate the rate of atmospheric CO(2) accumulation.

Errata: Net Primary Production in Tropical Forests: An Evaluation and Synthesis of Existing Field Data

Errata: Net Primary Production in Tropical Forests: An Evaluation and Synthesis of Existing Field Data

Net Primary Production in Tropical Forests: An Evaluation and Synthesis of Existing Field Data

Net Primary Production in Tropical Forests: An Evaluation and Synthesis of Existing Field Data

NET PRIMARY PRODUCTION IN TROPICAL FORESTS: AN EVALUATION AND SYNTHESIS OF EXISTING FIELD DATA

Information on net primary production in tropical forests is needed for the development of realistic global carbon budgets, for projecting how these ecosystems will be affected by climatic and atmospheric changes, and for evaluating eddy covariance mea- surements of tropical forest carbon flux. However, a review of the database commonly used to address these issues shows that it has serious flaws. In this paper we synthesize the data in the primary literature on NPP in old-growth tropical forests to produce a consistent data set on NPP for these forests. Studies in this biome have addressed only a few NPP com- ponents, all aboveground. Given the limited scope of the direct field measurements, we sought relationships in the existing data that allow estimation of unmeasured aspects of production from those that are more easily assessed. We found a predictive relationship between annual litterfall and aboveground biomass increment. For 39 diverse tropical forest sites, we then developed consistent, documented estimates of the upper and lower bounds around total NPP to serve as benchmarks for calibrating and validating biogeochemical models with respect to this biome. We developed these estimates based on existing field measurements, current understanding of aboveground consumption and biogenic volatile organic carbon emissions, and our judgment that belowground production is bounded by the range 0.2-1.2 3 ANPP (aboveground NPP). Across this broad spectrum of tropical forests (dry to wet, lowland to montane, nutrient-rich to nutrient-poor soils), our estimates of lower and upper bounds on total NPP range from 1.7 to 11.8 Mg C·ha 21 ·yr 21 (lower bounds) and from 3.1 to 21.7 Mg C·ha 21 ·yr 21 (upper bounds). We also showed that two relationships that have been used for estimating NPP (the Bray-Gorham relationship based on leaf litterfall and the Miami model based on temperature or precipitation) are not valid for the tropical forest biome.

Tropical rain forests as carbon sinks

Though since the early seventies the debate on the increase of carbon dioxide concentration in the atmosphere and its predicted impact on global climate has been the focus of many national, regional, and international discussions, and that deforestation in the tropics has been identified as one of the main contributing factors, very few detailed studies have actually been made on the primary production and rate of carbon storage/release of tropical forests. To appreciate the importance of tropical forests as carbon sinks, published data on carbon storage in tropical forest biomass, soil and litter were reviewed and synthesized. The data showed that: 1. 1) in the seventies, the total area of tropical forests of the world stood at about 1,628 × 10 6 hectares, of which about 58% or 1,043.90 × 10 6 hectares was contributed by tropical closed moist forests, and the remaining 42 % by savanna-type dry forests. 2. 2) Of the ca. 1,043.90 × 10 6 hectares of tropical closed moist forests, about 53.8% are located in Central and South America, 28% in Asia and Oceania, and 18.2% in Africa. 3. 3) Total storage of organic carbon (approximately equal to 50% of organic matter) amounted to 393.50 × 10 9 tonnes, with vegetation accounting for 58%, soil 41%, and litter 1%. Approximately 50% of the total storage was contributed by tropical moist and rain forests. 4. 4) Total litter production tropical forests was estimated at about 6.15 × 10 9 tonnes (Carbon), of which about 53% of was produced by tropical dry and moist rain forests, with the tropical moist rain forests accounted for about 30%. Turnover time of litter in tropical forests was less than 1.0 year. 5. 5) The rates of gross primary production in tropical forests ranged from 9.5 tonnes (Carbon)/ha/year in subtropical dry forests to 100 tonnes (Carbon)/ha/year in tropical moist rain forests; and that of net production from 5.5 tonnes (Carbon)/ha/year (Subtropical dry forests) to 36.0 tonnes (Carbon)/ha/year (lowland tropical moist forests) In conclusion, it may be restated that based on rather limited available data, tropical forests, particularly the undisturbed moist and rain forests, play an important role as carbon sinks in the global carbon cycle. These forests store about 46% of the world's living terrestrial carbon pool and about 11.55% of the world's soil carbon pool. Thus, any form of destruction (burning) or reduction in area of these forests will lead to a substantial increase of carbon dioxide concentration in the atmosphere. Notwithstanding this, it should be stressed that more accurate and up to date studies, using remotesensing techniques and ground surveys to establish the actual area of the remaining tropical forests and at the rate of which these forests are being eliminated annually are urgently needed. Equally wanting are in situ measurements of the rate of primary production and respiration of each of the forest types prevailing in tropical regions of the world.