ABSTRACT
BACKGROUND: The spruce forests are dominant communities in northwest China, and play a key role in national carbon budgets. However, the patterns of carbon stock distribution and accumulation potential across stand ages are poorly documented. METHODS: We investigated the carbon stocks in biomass and soil in the natural spruce forests in the region by surveys on 39 plots. Biomass of tree components were estimated using allometric equations previously established based on tree height and diameter at breast height, while biomass in understory (shrub and herb) and forest floor were determined by total harvesting method. Fine root biomass was estimated by soil coring technique. Carbon stocks in various biomass components and soil (0-100 cm) were estimated by analyzing the carbon content of each component. RESULTS: The results showed that carbon stock in these forest ecosystems can be as high as 510.1 t ha-1, with an average of 449.4 t ha-1. Carbon stock ranged from 28.1 to 93.9 t ha-1 and from 0.6 to 8.7 t ha-1 with stand ages in trees and deadwoods, respectively. The proportion of shrubs, herbs, fine roots, litter and deadwoods ranged from 0.1% to 1% of the total ecosystem carbon, and was age-independent. Fine roots and deadwood which contribute to about 2% of the biomass carbon should be attached considerable weight in the investigation of natural forests. Soil carbon stock did not show a changing trend with stand age, ranging from 254.2 to 420.0 t ha-1 with an average of 358.7 t ha-1. The average value of carbon sequestration potential for these forests was estimated as 29.4 t ha-1, with the lower aged ones being the dominant contributor. The maximum carbon sequestration rate was 2.47 t ha-1 year-1 appearing in the growth stage of 37-56 years. CONCLUSION: The carbon stock in biomass was the major contributor to the increment of carbon stock in ecosystems. Stand age is not a good predictor of soil carbon stocks and accurate evaluation of the soil carbon dynamics thus requires long-term monitoring in situ. The results not only revealed carbon stock status and dynamics in these natural forests but were helpful to understand the role of Natural Forest Protection project in forest carbon sequestration as well.
ABSTRACT
Sun-induced fluorescence (SIF) in the far-red region provides a new noninvasive measurement approach that has the potential to quantify dynamic changes in light-use efficiency and gross primary production (GPP). However, the mechanistic link between GPP and SIF is not completely understood. We analyzed the structural and functional factors controlling the emission of SIF at 760 nm (F760 ) in a Mediterranean grassland manipulated with nutrient addition of nitrogen (N), phosphorous (P) or nitrogen-phosphorous (NP). Using the soil-canopy observation of photosynthesis and energy (SCOPE) model, we investigated how nutrient-induced changes in canopy structure (i.e. changes in plant forms abundance that influence leaf inclination distribution function, LIDF) and functional traits (e.g. N content in dry mass of leaves, N%, Chlorophyll a+b concentration (Cab) and maximum carboxylation capacity (Vcmax )) affected the observed linear relationship between F760 and GPP. We conclude that the addition of nutrients imposed a change in the abundance of different plant forms and biochemistry of the canopy that controls F760 . Changes in canopy structure mainly control the GPP-F760 relationship, with a secondary effect of Cab and Vcmax . In order to exploit F760 data to model GPP at the global/regional scale, canopy structural variability, biodiversity and functional traits are important factors that have to be considered.
Subject(s)
Carbon Dioxide/metabolism , Grassland , Nitrogen/pharmacology , Phosphorus/pharmacology , Photosynthesis , Plant Leaves/anatomy & histology , Quantitative Trait, Heritable , Sunlight , Computer Simulation , Mediterranean Region , Photosynthesis/drug effects , Plant Leaves/drug effects , Plant Leaves/physiology , Seasons , Spectrometry, FluorescenceABSTRACT
Based on the data of the field investigation and laboratory and the database of the 8th national forestry inventory, ecosystem carbon density, storage amount, and sequestration potential of tree layer were estimated for five typical plantation ecosystems (Robinia pseudoacacia, Populus spp., Pinus tabuliformis Pinus armandii, which were grouped as one kind of ecosystems, Larix principis-rupprechtii, and Picea asperata) in Gansu Province. The results showed that the average carbon density and total carbon storage of the five typical plantation ecosystems were 139.65 t·hm-2 and 85.78 Tg, respectively. Ecosystem carbon density varied among ecosystems. It followed the sequence of premature (250.70 t·hm-2) > mature (175.97 t·hm-2) > middle-aged (156.92 t·hm-2) > young (117.56 t·hm-2) forest. Meanwhile, carbon storage in these plantations ranked in the order of young (45.47 Tg) > middle-aged (19.54 Tg) > mature (11.84 Tg) > pre-mature (8.93 Tg) forest. Specifically, young and middle-aged plantations contributed the most and accounted for 75.9% of the total carbon storage. The realistic carbon sequestration potential (CPr) by tree layer of the five typical plantation ecosystems in Gansu Province was estimated as 7.27 Tg. The two largest contributors toCPr were R. pseudoacacia (2.49 Tg) and Populus spp. (2.10 Tg). Young plantations (3.78 Tg) showed the largest CPr, followed by middle-aged plantations (2.04 Tg), and the value of premature plantations (0.45 Tg) was the smallest. The maximum carbon sequestration potential (CPmax) might be up to 27.55 Tg, the CPmax with different plantations ranked in the order of R. pseudoacacia (9.42 Tg)> L. principis-rupprechtii (6.22 Tg) ≈ P. asperata (6.36 Tg) > Populus spp. (3.18 Tg) >P. tabuliformis P. armandii (2.37 Tg). The CPmax of young and middle-aged plantations was estimated as 18.48 and 6.89 Tg, respectively, which accounted for 92% of the total maximum carbon sequestration potential.
