Abstract
Páramos, tropical alpine ecosystems, host one of the world’s most diverse alpine floras, account for the largest water reservoirs in the Andes, and some of the largest soil carbon pools worldwide. It is of global importance to understand the future of this extremely carbon-rich ecosystem in a warmer world and its role on global climate feedbacks. This study presents the result of the first in situ warming experiment in two Colombian páramos using Open-Top Chambers. We evaluated the response to warming of several ecosystem carbon balance-related processes, including decomposition, soil respiration, photosynthesis, plant productivity, and vegetation structure after 3 years of warming. We found that OTCs are an efficient warming method in the páramo, increasing mean air temperature by 1.7°C and mean daytime temperature by 3.4°C. The maximum air temperature differences between OTC and control was 23.1°C. Soil temperature increased only by 0.1°C. After 3 years of warming using 20 OTC (10 per páramo) in a randomized block design, we found no evidence that warming increased CO2 emissions from soil respiration, nor did it increase decomposition rate, photosynthesis or productivity in the two páramos studied. However, total C and N in the soil and vegetation structure are slowly changing as result of warming and changes are site dependent. In Sumapaz, shrubs, and graminoids cover increased in response to warming while in Matarredonda we observed an increase in lichen cover. Whether this change in vegetation might influence the carbon sequestration potential of the páramo needs to be further evaluated. Our results suggest that páramos ecosystems can resist an increase in temperature with no significant alteration of ecosystem carbon balance related processes in the short term. However, the long-term effect of warming could depend on the vegetation changes and how these changes alter the microbial soil composition and soil processes. The differential response among páramos suggest that the response to warming could be highly dependent on the initial conditions and therefore we urgently need more warming experiments in páramos to understand how specific site characteristics will affect their response to warming and their role in global climate feedbacks.
Highlights
The Earth is warming at an accelerated rate
open-top chambers (OTC) reduced air humidity resulting in higher values of vapor pressure deficit (VPD) in the OTC in comparison to the control plots all year round but specially in the dry season when highest VPD values paralleled with lowest soil water potential values (Figure 2)
Results from 3 years of in situ experimental warming using open-top chambers (OTC) at two páramo sites in Colombia shows that warming has not so far significantly increased soil respiration, litter decomposition, aboveground and belowground biomass, leaf-level photosynthesis, net ecosystem exchange or gross primary productivity, indicating that the páramo has some resilience to warming at least in the short-term
Summary
The Earth is warming at an accelerated rate. The temperature is projected to increase 1.0–4.8◦C by the end of this century (IPCC, 2014), with mountains experiencing a higher rise in temperature than the low-lands (Bradley et al, 2004, 2006). One piece of evidence that suggests vegetation is shifting in the mountain summits of the tropics comes from the work by Cuesta et al (2019) that documented important landscape transformations in the Andean highlands, including upward shifts of species and the formation of new communities in deglaciated forefronts (see Zimmer et al, 2018). The consequences of these changes on species distribution, carbon storage, and ecosystem services across Andean alpine ecosystems are a pressing question that needs to be addressed
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