Subtropical Pine Plantation Research Articles

Effects of thinning and understory removal on soil phosphorus fractions in subtropical pine plantations.

Forest management changes the physical environments and nutrient dynamics and then regulates the forest productivity. Soil phosphorus (P) availability is critical for productivity in tropical and subtropical forests. However, it was still poorly understood how soil P content and fraction respond to various forest management practices in these regions. Here, we measured the soil total P, available P, and Hedley's P fractions, including inorganic and organic P (Pi and Po), in subtropical pine plantations treated with understory removal (UR), non-dominant species thinning (NDST) and dominant species thinning (DST) after nine years. Compared to plantations without management (CK), treatments such as UR, NDST, and DST decreased soil total P at 0-10 cm and soil available P at 0-10 cm and 10-20 cm. Increases in resin-Pi, NaOH-Pi, and C.HCl-Pi resulted in a higher total Pi in 0-10 cm (p < 0.05) in treated plots (UR, NDST, and DST) than in CK plots. UR, NDST, and DST treatments increased NaHCO3-Po and NaOH-Po (p < 0.05) but decreased C.HCl-Po at a depth of 0-10 cm. Regardless of management treatments, soil total P, available P, and P fractions in 0-10 cm showed higher contents than those in 10-20 cm. There were positive relationships between total P and total Po (p < 0.01) and between available P and total Pi. There were also positive relationships between total P, available P, NaHCO3-Pi, and NaOH-Pi (p < 0.05). In conclusion, forest management such as UR, NDST, and DST decreased soil total P and available P, and transforming soil P fractions to available P will meet the P demand following management in the pine plantations of subtropical China.

Patterns of deep fine root and water utilization amongst trees, shrubs and herbs in subtropical pine plantations with seasonal droughts.

Seasonal droughts will become more severe and frequent under the context of global climate change, this would result in significant variations in the root distribution and water utilization patterns of plants. However, research on the determining factors of deep fine root and water utilization is limited. We measured the fine root biomass and water utilization of trees, shrubs and herbs, and soil properties, light transmission, and community structure parameters in subtropical pine plantations with seasonal droughts. We found that the proportion of deep fine roots (below 1 m depth) is only 0.2-5.1%, but that of deep soil water utilization can reach 20.9-38.6% during the dry season. Trees improve deep soil water capture capacity by enhancing their dominance in occupying deep soil volume, and enhance their deep resource foraging by increasing their branching capacity of absorptive roots. Shrubs and herbs showed different strategies for deep water competition: shrubs tend to exhibit a "conservative" strategy and tend to increase individual competitiveness, while herbs exhibited an "opportunistic" strategy and tend to increase variety and quantity to adapt to competitions. Our results improve our understanding of different deep fine root distribution and water use strategies between overstory trees and understory vegetations, and emphasize the importance of deep fine root in drought resistance as well as the roles of deep soil water utilization in shaping community assembly.

Effects of thinning on forest soil and stump respiration in a subtropical pine plantation

Thinning is an important forest management practice that can greatly affect ecosystem carbon budgets. However, few studies have reported the instant and prolonged effects of thinning under the same climate conditions, which is the scientific issue addressed by this study. The effects of thinning on soil physicochemical properties, soil respiration (RSoil), stump respiration (RStump) and carbon (C) release were quantified in a subtropical plantation based on parallel observations in Unthinned, 1-year post-thinning (PT1-yr) and 3-year post-thinning (PT3-yrs) treatments. Generally, the pH and NO3–-N decreased, and the NH4+-N and soil water contents (SWC) increased in PT1-yr and PT3-yrs. Soil temperature (T) decreased in PT1-yr and increased in PT3-yrs. Thinning promoted RSoil, but a slowdown of the promoting effects was found in PT3-yrs. Thinning continuously promoted RStump significantly; therefore, RStump in PT3-yrs > PT1-yr > Unthinned. The responses of RSoil and RStump to T and SWC changed after thinning. Among Unthinned, PT1-yr and PT3-yrs, the fitting surfaces for modeling the relations between RSoil and TSoil, SWCSoil became flatter. In contrast, the fitting surfaces become more curved for RStump and TStump, SWCStump. These results could be attributed to the complicated changes in the composition of respiration and the changing soil environment. The C release from the underlying surface increased year by year during the three years after thinning. The C released through RSoil was the dominant component. However, the C released through RStump determined the significant difference between C release in PT1-yr and PT3-yrs, which indicated the potential importance of RStump over time after thinning. As thinning is an important way to optimize the carbon sink function of global forests, extensive and intensive studies on thinning effects and the underlying mechanisms are necessary, which would be beneficial for an accurate estimation of forest carbon budgets under future climate change.

A genome-wide SNP genotyping resource for tropical pine tree species.

We performed gene and genome targeted SNP discovery towards the development of a genome-wide, multispecies genotyping array for tropical pines. Pooled RNA-seq data from shoots of seedlings from five tropical pine species was used to identify transcript-based SNPs resulting in 1.3million candidate Affymetrix SNP probe sets. In addition, we used a custom 40K probe set to perform capture-seq in pooled DNA from 81 provenances representing the natural ranges of six tropical pine species in Mexico and Central America resulting in 563K candidate SNP probe sets. Altogether, 300K RNA-seq (72%) and 120K capture-seq (28%) derived SNP probe sets were tiled on a 420K screening array that was used to genotype 576 trees representing the 81 provenances and commercial breeding material. Based on the screening array results, 50K SNPs were selected for commercial SNP array production including 20K polymorphic SNPs for P. patula, P. tecunumanii, P. oocarpa and P. caribaea, 15K for P. greggii and P. maximinoi, 13K for P. elliottii and 8K for P. pseudostrobus. We included 9.7K ancestry informative SNPs that will be valuable for species and hybrid discrimination. Of the 50K SNP markers, 25% are polymorphic in only one species, while 75% are shared by two or more species. The Pitro50K SNP chip will be useful for population genomics and molecular breeding in this group of pine species that, together with their hybrids, represent the majority of fast-growing tropical and subtropical pine plantations globally.

Interspecific competition for inorganic nitrogen between canopy trees and underlayer-planted young trees in subtropical pine plantations

Although the area of monospecific plantations in China ranks first in the world, these plantations possess poor disease resistance, low quality, and low ecological benefit. Planting broadleaf seedlings into the understory of monospecific coniferous plantations is an effective and common forest management method to improve plantation structures and enhance their resistance to adverse conditions, disease, and pests. Species that are desired and suitable are selected according to the complementarity of their functional traits to ensure optimal resource utilization and species coexistence. Thus, in Pinus massoniana and Pinus elliottii plantations where three broadleaf species were underplanted, any alterations to root functional traits and inorganic nitrogen (N) uptake rates in response to interspecific competition were studied in situ using 15N isotope labelling technology. The results showed that the five species preferred to absorb ammonium (dominant N form in native soils) rather than nitrate from the soil. Coniferous species showed higher plasticity in root biomass, physiology of N uptake rate, morphology, and mycorrhizal colonization than broadleaf species responding to interspecific competition. Coniferous trees reduced the investment in root biomass while enhanced N uptake rates to acclimate to belowground interspecific competition. Broadleaf species M. maudiae and S. superba were more dependent on mycorrhizal symbiosis to acquire resource in response to environmental variations. The amount of inorganic N uptake by P. massoniana and P. elliottii roots were inhibited by the presence of Michelia maudiae and Schima superba roots, respectively. Based on inorganic N uptake amount, M. maudiae and S. superba may be suitable for underplanting in the P. elliottii and P. massoniana plantations, respectively. Liquidambar formosana was suitable for both two pine plantations. The responses of root N uptake rate, mycorrhizal colonization and morphological traits to interspecific competition can provide supplemental data for species selection to improve structures of artificial plantations.

Below-ground determinants and ecological implications of shrub species' degree of isohydry in subtropical pine plantations.

The degree of plant iso/anisohydry is a popular framework for characterising species-specific drought responses. However, we know little about associations between below-ground and above-ground hydraulic traits as well as the broader ecological implications of this framework. For 24 understory shrub species in seasonally dry subtropical coniferous plantations, we investigated contributions of the degree of isohydry to species' resource economy strategies, abundance, and importance value, and quantified the hydraulic conductance (Kh ) of above-ground and below-ground organs, magnitude of deep water acquisition (WAdeep ), shallow absorptive root traits (diameter, specific root length, tissue density), and resource-use efficiencies (Amax , maximum photosynthesis rate; PNUE, photosynthetic nitrogen-use efficiency). The extreme isohydric understory species had lower wood density (a proxy for higher growth rates) because their higher WAdeep and whole-plant Kh allowed higher Amax and PNUE, and thus did not necessarily show lower abundance and importance values. Although species' Kh was coordinated with their water foraging capacity in shallow soil, the more acquisitive deep roots were more crucial than shallow roots in shaping species' extreme isohydric behaviour. Our results provide new insights into the mechanisms through which below-ground hydraulic traits, especially those of deep roots, determine species' degree of isohydry and economic strategies.

Root nitrogen acquisition strategy of trees and understory species in a subtropical pine plantation in southern China

Nitrogen (N) is considered as a major factor that limits plant growth and metabolism, and absorptive roots play a critical role in plant resource acquisition. However, little is known about the roles of mycorrhizal colonization, and morphological and architectural traits of absorptive roots in N uptake rates. We examined the uptake rates for ammonium ( $${\text{NH}}_{4}^{ + }$$ ), nitrate ( $${\text{NO}}_{3}^{ - }$$ ) and glycine using a 15N isotope tracer technique and measured mycorrhizal colonization rates and functional traits (morphology, architecture and chemistry) of absorptive roots in a subtropical plantation during the growing season. Results showed that trees, shrubs and herbs all preferred to take up $${\text{NH}}_{4}^{ + }$$ over $${\text{NO}}_{3}^{ - }$$ and glycine, likely due to the dominant available N form in native soils. Species coexisting in the subtropical plantation did not show chemical niche differentiation, but there was a temporal niche separation in N acquisition across plant species. Absorptive roots with higher mycorrhizal colonization rates exhibited higher N uptake rates than those with lower colonization. In May, morphological traits (diameter and root tissue density) seemed playing important roles in N acquisition on that the absorptive roots with larger diameter and shorter specific root length (SRL) showed higher uptake rates for $${\text{NH}}_{4}^{ + }$$ , $${\text{NO}}_{3}^{ - }$$ , and glycine than those with smaller diameter and longer SRL. While in August, the architectural traits of root branching might be essential to enhance nutrient absorption on that the absorptive roots with intensive branching exhibited higher N uptake rates than those with less branching. Our findings suggested that plant species may evolve effective N acquisition strategies integrated mycorrhizal symbiosis, and root morphological and architectural traits over a temporal scale to acclimate to the changing environments.

Linking reliance on deep soil water to resource economy strategies and abundance among coexisting understorey shrub species in subtropical pine plantations

Strategies for deep soil water acquisition (WAdeep ) are critical to a species' adaptation to drought. However, it is unknown how WAdeep determines the abundance and resource economy strategies of understorey shrub species. With data from 13 understorey shrub species in subtropical coniferous plantations, we investigated associations between the magnitude of WAdeep , the seasonal plasticity of WAdeep , midday leaf water potential (Ψmd ), species abundance and resource economic traits across organs. Higher capacity for WAdeep was associated with higher intrinsic water use efficiency, but was not necessary for maintaining higher Ψmd in the dry season nor was it an ubiquitous trait possessed by the most common shrub species. Species with higher seasonal plasticity of WAdeep had lower wood density, indicating that fast species had higher plasticity in deep soil resource acquisition. However, the magnitude and plasticity of WAdeep were not related to shallow fine root economy traits, suggesting independent dimensions of soil resource acquisition between deep and shallow soil. Our results provide new insights into the mechanisms through which the magnitude and plasticity of WAdeep interact with shallow soil and aboveground resource acquisition traits to integrate the whole-plant economic spectrum and, thus, community assembly processes.

Effect of nitrogen addition and litter removal on understory vegetation, soil mesofauna, and litter decomposition in loblolly pine plantations in subtropical Argentina

Loblolly pine monocultures have been increasingly expanding in the Atlantic Forest of South America especially in northern Argentina. Pine plantations can modify understory vegetation and soil characteristics due to the management practices and to the dense mulch of pine needles that develop in the forest floor that could affect soil biota and ecosystem processes. Nitrogen (N) addition as expected as atmospheric deposition can also contribute to these changes. The aim of this study was to assess the effect of litter removal and low levels of N addition on understory regeneration, soil mesofauna abundance, and leaf litter decomposition. For this purpose, a completely randomized block design was used. Nitrogen addition had significant effects on understory regeneration promoting creeping herbs, graminoids and shrubs life forms affecting tree establishment and growth. Litter removal treatment showed the same pattern but only promoting the creeping herbs that could also have affected tree species. Decomposition decreased due to litter removal and was slightly increased by N addition. The addition of N decreased the abundance of mesofauna in the mulch, especially Symphypleone (a suborder of Collembola), but the abundance of the soil communities was not affected. Litter removal had a strong impact on these communities because most individuals and species of the mesofauna are present in the litter and not in the soil. This is one of the first studies analyzing the effect of low amounts of N addition and litter removal in subtropical pine plantations and contribute to understand potential impacts of increasing N deposition on biodiversity and soil processes, and to select organisms that may help as bioindicators in assessing impacts on ecological functions in productive ecosystems.

Nitrogen additions inhibit nitrification in acidic soils in a subtropical pine plantation: effects of soil pH and compositional shifts in microbial groups

Plantation forests play a pivotal role in carbon sequestration in terrestrial ecosystems, but enhanced nitrogen (N) deposition in these forests may affect plantation productivity by altering soil N cycling. Hence, understanding how simulated N deposition affects the rate and direction of soil N transformation is critically important in predicting responses of plantation productivity in the context of N loading. This study reports the effects of N addition rate (0, 40, and 120 kg N ha−1 a−1) and form (NH4Cl vs. NaNO3) on net N mineralization and nitrification estimated by in situ soil core incubation and on-soil microbial biomass determined by the phospholipid fatty acid (PLFA) method in a subtropical pine plantation. N additions had no influences on net N mineralization throughout the year. Net nitrification rate was significantly reduced by additions of both NH4Cl (71.5) and NaNO3 (47.1%) during the active growing season, with the stronger inhibitory effect at high N rates. Soil pH was markedly decreased by 0.16 units by NH4Cl additions. N inputs significantly decreased the ratio of fungal-to-bacterial PLFAs on average by 0.28 (49.1%) in November. Under NH4Cl additions, nitrification was positively related with fungal biomass and soil pH. Under NaNO3 additions, nitrification was positively related with all microbial groups except for bacterial biomass. We conclude that simulated N deposition inhibited net nitrification in the acidic soils of a subtropical plantation forest in China, primarily due to accelerated soil acidification and compositional shifts in microbial functional groups. These findings may facilitate a better mechanistic understanding of soil N cycling in the context of N loading.

Carbon and water vapor balance in a subtropical pine plantation

Abstract: Afforestation has been proposed as an effective tool for protecting primary and/or secondary forests and for mitigating atmospheric CO2. However, the dynamics of primary productivity differs between plantations and natural forests. The objective of this work was to evaluate the potential for carbon storage of a commercial pine plantation by determining its carbon balance. Measurements started when trees were aged 6 and ended when they were older than 8 years. We measured CO2 and water vapor concentrations using the Eddy covariance method. Gross primary productivity in 2010 and 2011 was 4290 ± 473 g C m-2 and 4015 ± 485 g C m-2, respectively. Ecosystem respiration ranged between 7 and 20 g C m-2 d-1, reaching peaks in all Februaries. Of the 30 months monitored, the plantation acted as carbon source for 21 months and as carbon sink for 6 months, while values close to neutrality were obtained during 3 months. The positive balance representing CO2 loss by the system was most likely due to the cut branches left on the ground following pruning activities. The plantation was subjected to pruning in January and September 2008 and to sanitary pruning in October 2010. In all cases, cut branches were not removed but remained on the ground. Residue management seems to have a very important impact on carbon balance.

Estimating groundwater evapotranspiration by a subtropical pine plantation using diurnal water table fluctuations: Implications from night-time water use

Exotic pine plantations have replaced large areas of the native forests for timber production in the subtropical coastal Australia. To evaluate potential impacts of changes in vegetation on local groundwater discharge, we estimated groundwater evapotranspiration (ETg) by the pine plantation using diurnal water table fluctuations for the dry season of 2012 from August 1st to December 31st. The modified White method was used to estimate the ETg, considering the night-time water use by pine trees (Tn). Depth-dependent specific yields were also determined both experimentally and numerically for estimation of ETg. Night-time water use by pine trees was comprehensively investigated using a combination of groundwater level, sap flow, tree growth, specific yield, soil matric potential and climatic variables measurements. Results reveal a constant average transpiration flux of 0.02mmh−1 at the plot scale from 23:00 to 05:00 during the study period, which verified the presence of night-time water use. The total ETg for the period investigated was 259.0mm with an accumulated Tn of 64.5mm, resulting in an error of 25% on accumulated evapotranspiration from the groundwater if night-time water use was neglected. The results indicate that the development of commercial pine plantations may result in groundwater losses in these areas. It is also recommended that any future application of diurnal water table fluctuation based methods investigate the validity of the zero night-time water use assumption prior to use.

Nitrogen addition regulates tradeoff between root capture and foliar resorption of nitrogen and phosphorus in a subtropical pine plantation

Increased nitrogen availability affects root capture and leaf resorption of nitrogen and phosphorus, and the corresponding acquisition-conservation tradeoff in slash pine forests. Plants may maintain their stoichiometric homeostasis via regulating root nutrient capture (acquisition) and leaf nutrient resorption (conservation). However, how increased nitrogen (N) availability affects root capture and leaf resorption of N and phosphorus (P), and the corresponding acquisition-conservation tradeoff remains unclear. We quantified N and P concentrations and their stoichiometric ratios of five nutrient pools (soils, absorptive fine-roots, transport fine-roots, green needles, and senesced needles) to investigate simultaneous responses of root capture (nutrient foraging potential and translocation) and needle resorption (efficiency and proficiency) to different rates and forms of N addition in a slash pine plantation in subtropical China. N addition increased N concentration in senesced needles, but reduced N capture capacity. N addition reduced P concentration in senesced needles (improved P resorption proficiency), but did not affect P capture capacity. N addition exerted no significant influence on resorption efficiency of N and P. N rate and form effects occurred only in nutrient foraging (N foraging was more responsive to high N rate and P foraging was more responsive to ammonium-based N addition), but not in nutrient translocation and resorption. The decreased root N capture capacity and increased senesced needle N concentration imply an alleviation of N limitation to plant growth and a behavior of plants to economize on cost for nutrient acquisition and conservation. P resorption rather than capture strategy was employed, indicating a more conservative use of P in response to exacerbated P limitation. These findings jointly suggest that the allocation of effort towards capture and resorption strategy depends on the strength and type of nutrient limitation. Our results have implications for understanding the acquisition-conservation tradeoff in plant nutrient economy and the mechanisms that plants maintain their stoichiometric homeostasis in the context of N loading.

Effects of mixture of branch order-based roots and nitrogen addition on root decay in a subtropical pine plantation

Non-additive effects may occur when branching order-based fine roots decompose in mixture, due to their distinct chemical composition. However, these effects and how they respond to increased nitrogen (N) availability are poorly known. We conducted a 524-day field litterbag experiment to examine the potential non-additive effects of order-based fine root decomposition and their responses to different rates of N addition in a Pinus elliottii (slash pine) plantation in China. The intact fine roots of slash pine trees were hierarchically dissected and split into two groups (lower-order roots (the first and second order roots) and higher-order roots (the third to fifth order roots)). The decomposition of these two root groups was monitored either separately or in 1:1 mixture. The non-additive effects did not occur when the two root groups decomposed in mixture. However, high rate of N addition shifted the root group interactions from additive to synergistic effects through contrasting effects on individual root group (lower-order roots). High rate of N addition retarded the decomposition of lower-order roots more in isolation than in mixture, due to the decreased binding of acid-unhydrolyzable residue to inorganic N ions in mixture. Therefore, we suggest that although stoichiometric heterogeneity holds within the branching hierarchy of fine roots, the tight coupling of N with acid-unhydrolyzable residue of root tissues may limit N use by microdecomposers, and thereby causing the additive effect. Since the mixing effect of order-based root decomposition is affected by N addition, understanding the chemical heterogeneity within fine root systems and their linkage with ambient N availability during decomposition either in isolation or in mixture may facilitate the accurate prediction of root decomposition responses to N loading.

Low Nitrogen Retention in Soil and Litter under Conditions without Plants in a Subtropical Pine Plantation

Soil acts as a major sink for added nitrogen (N) in forests, but it remains unclear about the capacity of soil to immobilize N under conditions without plant roots and whether added N interacts with ecosystem N to affect N retention. We added 15NH415NO3 to in situ soil columns (with leaching) and leaf litter (without leaching) of two tree species in a subtropical Pinus elliottii plantation. Soil and litter were collected three or eight months after N addition to measure concentrations of indigenous and exogenous N. About 70% of exogenous N was retained in soil three months after N addition, of which 65.9% were in inorganic forms. Eight months after N addition, 16.0% of exogenous N was retained in soil and 9.8%–13.6% was immobilized in litter. N addition increased the mineral release and nitrification of soil indigenous N. Loss of litter indigenous N was also increased by N addition. Our results suggest that N deposition on lands with low root activities or low soil carbon (C) contents may lead to increased N output due to low N immobilization. Moreover, the effects of added N on ecosystem indigenous N may decrease the capacity of soil and litter in N retention.

Effect of temperature on woodwasp (Sirex noctilio F.) development and parasitism by the entomopathogenic nematode, Deladenus siricidicola

The woodwasp, Sirex noctilio, is a significant global pest of exotic pine plantations in the Southern Hemisphere and now threatens native pine forests in North America. Management in Australia relies on biocontrol using the nematode, Deladenus (=Beddingia) siricidicola (Bedding), which infects and sterilises females who then further disperse the nematode. This pest is spreading into warmer regions in Australia and South America and coupled with the threat of global climate change, there is uncertainty as to how increasing temperatures will affect the biocontrol program. S.noctilio within nematode-inoculated wood were reared at four temperatures (24, 25.3, 26.6 and 28°C) to investigate the effects of elevated temperatures on wasp development (emergence time, sex ratio and size), development of eggs (number, size, and maturation) and infection by the nematode. At 24°C, which reflects current field temperature, S. noctilio were bigger in size and all the eggs were normal and all were infected with nematodes. Modest rises in temperature reflecting climate change scenarios resulted in smaller sized S. noctilio, disrupted egg development and maturation, and lowered the nematode sterilisation rate in females. Reduced S. noctilio female body size and egg infection will likely compromise biocontrol by D. siricidicola in its current distribution, but disrupted egg development may act directly on the pest, limiting dispersal of S. noctilio into subtropical pine plantations and adaptation to climate change.

Effect of litter layer on soil–atmosphere N2O flux of a subtropical pine plantation in China

Forest soils are important sources for nitrous oxide (N2O), but how the surface litter layer affects these sources is still unclear. Seasonal rainfall in the subtropical monsoon climate provides a unique opportunity to examine soil–atmosphere N2O flux under a wide range of soil water content. We studied this question over 3 years using a litter removal method in a 20-year-old pine plantation (Pinus elliottii) in subtropical China. Annual mean chamber-based soil–atmosphere N2O fluxes of the control (FCK) and litter-free (FLF) treatments were 6.07 and 5.17 μg N2O m−2 h−1, respectively. Removal of the litter layer reduced 15% of soil N2O emissions, suggesting the mineral soil as the dominant factor that determines soil N2O emissions. Seasonal FCK and FLF were both significantly influenced by water-filled pore space (WFPS) but not by soil temperature (TS). However, FCK and FLF were both correlated with TS during the wet season (January–June) but not during the dry season (July–December). During the wet season, FCK and FLF were 84% and 132% higher than during the dry season, respectively. In contrast, seasonal litter-based N2O fluxes (FCK−LF = FCK − FLF) were not correlated with WFPS and TS. During the dry season, however, a positive relationship was observed for FCK−LF and WFPS. In the context of climate change and human activities, future changes in soil environment and surface litter management will alter the strength of soil N2O emissions of the subtropical pine forests in China.

The litter layer acts as a moisture-induced bidirectional buffer for atmospheric methane uptake by soil of a subtropical pine plantation

Forest soils are well known sinks for atmospheric methane (CH4), but how the surface litter layer controls gas diffusion into the mineral soil is still unclear. Seasonal rainfall in the humid climate provides a unique opportunity to examine uptake of atmospheric CH4 under a wide range of soil water content (SWC). We studied this question using a litter removal method in a 20-year-old slash pine (Pinus elliottii) plantation in subtropical China during 2005–2007. Soil-atmosphere CH4 fluxes of the control (FCK) and litter-free (FLF) treatments and their differences (litter-affected CH4 flux, FCK–LF = FCK − FLF) were all significantly influenced by SWC and not by soil temperature. Litter layer reduced atmospheric CH4 uptake by soil when SWC was below 15.8 vol%, and increased atmospheric CH4 consumption by soil when SWC was above this value. We concluded that the litter layer acts as a moisture-induced bidirectional buffer for atmospheric CH4 uptake by soils in a subtropical humid pine plantation. However, the removal of the litter layer had a minimal effect (+0.7%) on annual atmospheric CH4 uptake by soil, through compensating effects during the wet and dry seasons. Therefore, in the context of climate change, future changes in SWC will alter the strength of atmospheric CH4 uptake by soils of subtropical pine plantations.

Adaptation of tropical and subtropical pine plantation forestry to climate change: Realignment of Pinus patula and Pinus tecunumanii genotypes to 2020 planting site climates

Pinus patula and Pinus tecunumanii, two pines native to Mexico and Central America, are important plantation species for the forestry sector in the tropics and subtropics. In recent decades, members of the International Tree Conservation & Domestication Program (CAMCORE), North Carolina State University, have established large, multisite provenance trials for these pine species. The data provide valuable information about species and provenance choice for plantation establishment in many regions with different climates. However, since climate is changing rapidly, it may become increasingly difficult to choose the right species and provenance to plant. The aim of this study is to test the suitability of seed material under changing climate of two P. patula varieties (P. patula var. patula and P. patula var. longipedunculata) and two P. tecunumanii ecotypes (highland and lowland). For each variety and ecotype, a site quality model was developed that statistically relates growth to environmental factors and couples the predictions to the average 2020 climate prediction of four general circulation models. Three developed models were significant and robust. Provenances of P. tecunumanii from lowland areas in Central America are expected to be most productive in 2020 because of their promising performance under rather hot and wet climates.

Nutrient dynamics in decomposing needles ofPinus luchuensisafter typhoon disturbance in a subtropical environment

La decomposition des chutes d'aiguilles normales et occasionnees par un typhon et leur modele de liberation des nutriments ont ete etudies pour 10 elements (C, N, P, K, Ca, Mg, S, Fe, Al et Mn). L'etude a ete faite dans une plantation de pin (Pinus luchensis Mayr.) a Okinawa (SO du Japon). Elle a dure 3 ans et a utilise la technique des bacs a litiere. Apres 3 ans les taux de decomposition etaient de 0,361 et 0,323 an -1 respectivement pour les chutes d'aiguilles liees au typhon et les chutes normales d'aiguilles. Les chutes aiguilles liees au typhon se decomposent significativement plus rapidement que les chutes normales d'aiguilles, ce qui est du a une plus forte concentration en N et P. Les modeles de transfert des elements varient fortement. Toutefois, des differences significatives dans les modeles de dynamique de masse des elements entre les deux types de chute d'aiguille ont seulement ete mises en evidence pour N et P (P Ca≥Mg≥C>S≥N≥Mn>P» Fe ≥ Al. Une decomposition rapide avec une liberation rapide de P et N pour les aiguilles dont la chute a ete occasionnee par le typhon indique que la perturbation par le typhon peut conduire le cycle de P et N a un taux quelque peu plus rapide, ce qui est important du point de vue de la productivite de la foret puisque P et N sont des nutriments limitants dans les forets subtropicales d'Okinawa.