Leaf litter stoichiometry affects decomposition rates and nutrient dynamics in tropical forests under restoration in Costa Rica

Responses of carbon, nitrogen, and phosphorus contents and stoichiometry in soil and fine roots to natural vegetation restoration in a tropical mountainous area, Southern China

The stoichiometry of key elements such as C, N, and P is an important indicator of ecosystem nutrient status and biogeochemical cycling. Nevertheless, the responses of soil and plant C:N:P stoichiometric characteristics to natural vegetation restoration remain poorly understood. In this study, we investigated C, N, and P contents and stoichiometry in soil and fine roots along vegetation restoration stages (grassland, shrubland, secondary forest, and primary forest) in a tropical mountainous area in southern China. We found that soil organic carbon, total N, C:P ratio, and N:P ratio significantly increased with vegetation restoration and significantly decreased with increasing soil depth, whereas there was no significant effect on soil total P and C:N ratio. Furthermore, vegetation restoration significantly increased the fine root N and P content and N:P ratio, whereas soil depth significantly decreased the fine root N content and increased the C:N ratio. The increasing average N:P ratio in fine roots from 17.59 to 21.45 suggested that P limitation increased with vegetation restoration. There were many significant correlations between C, N, and P contents and their ratios in soil and fine roots, indicating a reciprocal control of nutrient stoichiometric characteristics between them. These results contribute to our understanding of changes in soil and plant nutrient status and biogeochemical cycling during vegetation restoration and provide valuable information for restoration and management of tropical ecosystems.

Implications of Foliar Particulate Matter Deposition on the Physiology and Nutrient Allocation of Dominant Perennial Species of the Indo-Gangetic Plains

The ramifications of different concentrations of foliar particulate matter on the physiology, nutrient stoichiometry, allocation pattern, and their corresponding re-translocation rates were investigated for evergreen (Mangifera indica and Psidium guajava), semi-evergreen (Ficus religiosa and Azadirachta indica), and deciduous (Dalbergia sissoo) tree species in a simulation experiment over an exposure period of 2 years. Physiological parameters (P_n, g_s, Ci, E, and WUE), nutrient stoichiometry (C: N) in different plant parts, and their allocation pattern for five macro- (C, N, K, Mg, Ca) and five (Zn, Ni, Mn, Cu, Fe) micro-elements at two different concentrations of particulate matter (ambient and elevated) with respect to control (no particulate load) were assessed. Significant differences in nutrient concentrations and their re-translocation rates were observed between the treatments in evergreen species compared to deciduous species. The photosynthetic rate significantly declined with an increase in foliar deposition of particulate matter. Higher variations in C, N, K, Mg, and Zn levels were found compared to other elements under particulate matter stress and the ratio of C/N showed a slight decline in mature leaves except in deciduous tree species. The nutrient stoichiometry revealed that the deciduous species were more tolerant whereas the re-translocation efficiency was maximum for the semi-evergreen tree species. The nutrient allocation was found greater in foliage compared to branch in evergreen and was opposite in semi-evergreen and deciduous tree species. The element re-translocation rate indicated an inconsistent behavior in nutrient recycling under the particulate matter load depending upon the tree species. The study entrenched a critical change in nutrient re-translocation and allocation pattern under the particulate stress in different parts of the tree, suggesting a novel approach for screening the tree species for sustainable plantation and planning of urban areas.

Effects of Fertilization and Dry-Season Irrigation on Litterfall Dynamics and Decomposition Processes in Subtropical Eucalyptus Plantations

Nutrient management in Eucalyptus plantations is critical for wood production and sustainable development. The biogeochemical mechanisms in Eucalyptus plantations are not fully understood due to changes in the spatiotemporal pattern of precipitation and plantation management. The nutrients released from litterfall are important sources of soil nutrition. We measured the seasonal production of various litterfall types and the proportions of their released nutrients in Eucalyptus urophylla × E. grandis plantations under compound fertilization, dry-season irrigation, and a combined compound fertilization and dry-season irrigation treatment. Our results showed that fertilization increased aboveground biomass and annual litterfall production (except leaf), and that the peak of litterfall production occurred in the rainy season. We found that the decomposition rates of leaf were significantly higher than that of twig, which were mainly controlled by stoichiometric characteristics, followed by soil enzyme activity (β-glucosidase, urease, and polyphenol oxidase). Fertilization decreased the carbon: nitrogen ratio and carbon: phosphorus ratio in litter, and increased soil enzyme activities, which accelerates litter decomposition and nutrient release. Dry-season irrigation increased litter decomposition and only affected the proportion of released potassium by changing the carbon: potassium ratio. Fertilization and dry-season irrigation accelerated the nutrient cycle to enhance compensatory growth. These results help to comprehend the effects of forest management on litterfall dynamics and decomposition processes in Eucalyptus plantations with seasonal drought.

Grazing and Mowing Affect the Carbon-to-Nitrogen Ratio of Plants by Changing the Soil Available Nitrogen Content and Soil Moisture on the Meadow Steppe, China

Common grassland management practices affect plant and soil element stoichiometry, but the primary environmental factors driving variation in plant C/N ratios for different species in different types of grassland management remain poorly understood. We examined the three dominant C/N stoichiometric responses of plants to different land uses (moderate grazing and mowing) in the temperate meadow steppe of northern China. Our results showed that the responses of the C/N ratio of dominant plants differed according to the management practice. The relative abundance of N in plant tissues increased due to increased soil NO₃⁻, with a consequent decrease in plant C: N in the shoots of Leymus chinensis, but the C/N ratio and nitrogen concentration in the shoots of Bromus inermis and Potentilla bifurca were relatively stable under short-term moderate grazing management. Mowing reduced the concentration of soil NH₄⁺, thus reducing the nitrogen concentration of the roots, resulting in a decrease in the root C/N ratio of Potentilla bifurca. Structural equation model (SEM) showed that the root C/N ratio was affected by both root N and soil inorganic N, while shoot C/N ratio was only affected by the soil inorganic N. Our findings provide a mechanistic understanding of the responses of plant C/N ratio to land use change. The species-level responses of plant stoichiometry to human-managed grasslands deserve more attention.

Influence of scattered trees in grazing areas on soil properties in the Piedmont region of the Colombian Amazon

Trees dispersed in grazing areas are contribute to the sustainability of livestock systems. The interactions between trees and soil are ecological processes that allow the modification of the biology, fertility, and physics of the soil. This study was aimed to assess the influence of dispersed trees in pastures on soil properties in grazing areas for dual-purpose cattle systems in the Piedmont region of the Colombian Amazon. The work was done in grazing areas with scattered trees at the Centro de Investigaciones Amazónicas CIMAZ–Macagual in Florencia—Caquetá—Colombia. We evaluated the effect of five tree species, Andira inermis, Bellucia pentámera, Guarea Guidonia, Psidium guajava and Zygia longifolia, on soil properties (up to 30 cm soil depth) under and outside the influence of the crown. Under the tree crown, three points were systematically taken in different cardinal positions. This was done at a distance corresponding to half the radius of the tree crown. The sampling points in the open pasture area (out of crown) were made in the same way, but at 15 m from the crown border. The ANOVA showed significant interaction (P < 0.0001) between tree species and location for macrofauna abundance up to 30 cm soil depth. For this reason, we performed the comparison between locations for each tree species. Chemical soil variables up to 10 cm soil depth only showed interaction of tree species-location for exchangeable potassium (P = 0.0004). Soil physical soil characteristics up to 30 cm soil depth only showed interaction of tree species-location at 20 cm soil depth (P = 0.0003). The principal component analysis for soil properties explained 61.1% of the total variability of the data with the two first axes. Using Monte Carlo test, we found crown effect for all species. Trees help to control exchangeable mineral elements that can affect the soil, potentiate basic cations such as magnesium and potassium, increase the abundance of soil macrofauna; but some trees with high ground level of shade in grazing areas could increase soil compaction due to the greater concentration of cattle in these areas.

Ecological stoichiometric characteristics of soil-moss C, N, and P in restoration stages of karst rocky desertification

Rocky desertification is the most serious ecological disaster in karst areas. Comprehensive control of rocky desertification plays an important role in promoting the economic development of karst areas. Studying the stoichiometric characteristics of mosses and soil can provide a powerful reference for the ecological restoration and evaluation of ecosystems experiencing rocky desertification. Soil and mosses were collected from sites representing different stages of ecological restoration (bare rock, grassland, shrubland, and secondary forest), and the contents of carbon (C), nitrogen (N), and phosphorus (P) were detected for ecological stoichiometric analysis. The results indicate that in different restoration stages following karst rocky desertification, the contents of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) and the stoichiometric ratios in the shrub habitat are higher than those in the bare rock, grassland, and secondary forest habitats. However, the TP and available P contents were low at all stages (0.06 g/kg and 0.62 mg/kg, respectively). The N and P contents and stoichiometric ratios in the mosses showed no significant differences among the succession stages. The C contents in the mosses had a significant positive correlation with SOC and TN and TP content, and the P content had a significant positive correlation with the soil available P. However, there was a significant negative correlation between the C: N and C:P ratios of the bryophytes and soil C: N. In summary, during the process of natural restoration of karst rocky desertification areas, SOC and soil TN contents accumulate with each succession stage. Soil nutrients are higher in shrub habitats than in other succession stages. Mosses have a strong effect on improving soil nutrients in rocky desertification areas.

Decomposition and nutrient release from the mixed leaf litter of three agroforestry species in the Sudanian zone of West Africa

This study was carried out to determine the rates of decomposition and nutrient release from pure and mixed leaf litter samples of three agroforestry species (Azolla africana Desv., Detarium microcarpum Guill. and Perr. and Vitellaria paradoxa C.F.Gaertn.) that have potential use as green manure. Litterbags containing a total of 5 g of pure and mixed leaf litter of different quality levels were incubated under field conditions from July to November in 2017. Litter decomposition and nutrient release (N, P, and K) rates were assessed in each litterbag. The decomposition rate (k) indicated that pure A. africana litter decomposed faster (k = 0.406 week−1) than its mixture with V. paradoxa (k = 0.114 week−1) and D. microcarpum (k = 0.103 week−1). The slowest decomposition rates were found for the pure D. microcarpum (k = 0.075 week−1) and V. paradoxa (k = 0.071 week−1) leaf litters. Mixing with A. africana litter increased the decomposition rate of both D. microcarpum and V. paradoxa leaf litter. We conclude that mixing litter of different quality can accelerate the decomposition of pure litter with poor quality and represents a practical biomass management option for farmers to improve nutrient cycling in agroforestry systems.