Trade-Offs Among Aboveground, Belowground, and Soil Organic Carbon Stocks Along Altitudinal Gradients in Andean Tropical Montane Forests

Abstract

Tropical montane forests (TMFs) play an important role as a carbon reservoir at a global scale. However, there is a lack of a comprehensive understanding on the variation in carbon storage across TMF compartments [namely aboveground biomass (AGB), belowground biomass (BGB), and soil organic matter] along altitudinal and environmental gradients and their potential trade-offs. This study aims to: 1) understand how carbon stocks vary along altitudinal gradients in Andean TMFs, and; 2) determine the influence of climate, particularly precipitation seasonality, on the distribution of carbon stocks across different forest compartments. The study was conducted in sixty 0.1 ha plots along two altitudinal gradients at the Podocarpus National Park (Ecuador) and Río Abiseo National Park (Peru). At each plot, we calculated the amount of carbon in AGB (i.e. aboveground carbon stock, AGC), BGB (i.e. belowground carbon stock, BGC), and soil organic matter (i.e. soil organic carbon stock, SOC). The mean total carbon stock was 244.76 ± 80.38 Mg ha -1 and 211.51 ± 46.95 Mg ha -1 in the Ecuadorian and Peruvian plots, respectively. Although AGC, BGC, and SOC showed different partitioning patterns along the altitudinal gradient both in Ecuador and Peru, total carbon stock did not change with altitude in either site. The combination of annual mean temperature and precipitation seasonality explained differences in the observed patterns of carbon stocks across forest compartments between the two sites. This study suggests that the greater precipitation seasonality of colder, higher altitudes may promote faster turnover rates of organic matter and nutrients and, consequently, less accumulation of SOC but greater AGC and BGC, compared to those sites with lesser precipitation seasonality. Our results demonstrate the capacity of TMFs to store substantial amounts of carbon and suggest the existence of a

Soil respiration variation along an altitudinal gradient in the Italian Alps: Disentangling forest structure and temperature effects

“…These values were within the ranges reported by other studies along elevation gradients [ 28 , 64 ]. The lowest value was recorded at the lowest elevation, and our data corroborated an increase of the soil organic C stock with increasing elevation shown in other studies [ 9 , 26 , 27 , 29 , 64 – 67 ]. Being the main driver for the loss of soil organic C, low temperature can limit the decomposition of organic matter at high elevations.…”

“…One of the main factors affecting soil bulk density is SOC content [ 81 ]. Therefore, the lowest values of soil bulk density at high elevation could be explained by the high stock of SOC, as confirmed by the negative association found between SOC stock and soil bulk density ( Table 3 ), previously reported in other studies [ 9 , 64 , 67 , 82 ].…”

“…Being the main driver for the loss of soil organic C, low temperature can limit the decomposition of organic matter at high elevations. For this reason, elevation could induce a significant increase in SOC [ 25 , 65 , 67 – 69 ]. However, an increment in SOC stock was not linearly linked with elevation gradient and, therefore, our first hypothesis was not confirmed.…”

Soil respiration variation along an altitudinal gradient in Italian Alps: Disentangling forest structure and temperature effects

“…Overall, our data confirms an increase of the soil organic C stock in soil with increasing elevation [7,24, 25,27,59,60,61,62]. The low temperature can limit the decomposition of organic matter at high altitudes, as the temperature is the main driver for the loss of the soil organic C. For this reason, altitude could induce a significant increase in SOM [23,59,62,63,63]. However, SOM increment was not linear along the elevation gradient and therefore, our first hypothesis was not confirmed.…”

“…One of the main factors affecting soil bulk density is SOM content [74]. Therefore, the lowest values of soil bulk density at high elevation could be explained by the high amount of soil C, as confirmed by the negative association found between soil C and soil bulk density (Table 3), previously reported in other studies [7, 61,62,75].…”