"The complexity of decomposer communities is a fundamental component of forest biodiversity, yet it has long been overlooked by the academic community." Dr. Luan Junwei, a researcher at the International Bamboo and Rattan Organization, developed an interest in studying the relationship between biodiversity and ecosystem functioning during his studies in Canada eleven years ago.
On March 18th, collaborating with Dr. Liu Shirong, a researcher at the Chinese Academy of Forestry, and his team, who is also an academician of the Chinese Academy of Engineering, they published their latest research findings in the Proceedings of the National Academy of Sciences (PNAS) in the United States. Their study reveals the crucial role of forest ecosystem biodiversity in mitigating the impacts of climate change and proposes that biodiversity in decomposition systems can alleviate the effects of drought on inter-regional biological communities.
The Baotianman Nature Reserve Oak Forest Drought Simulation Experiment Platform was established in 2013 in Henan Province. Image provided by Junwei Luan.
This research provides compelling evidence internationally, for the first time from the perspective of ecosystem decomposition processes, regarding the negative impacts of biodiversity on key ecosystem functions such as mitigating climate change effects on biosphere-atmosphere carbon exchange and nutrient cycling.
Reviewers of the paper noted that it is a well-thought-out and excellently executed study on an important topic in ecosystem ecology. The findings timely offer crucial insights into forest ecosystem nutrient and carbon cycling changes caused by biodiversity loss and climate change.
Central Mystery: Forest Litter Decomposition
In forest ecosystems, producers, consumers, and decomposers play distinct roles. Producers convert solar energy into chemical energy through photosynthesis, providing the energy and material foundation for the entire ecosystem; consumers acquire energy and nutrients by consuming plants or other animals, facilitating the transfer of matter and energy; decomposers break down organic matter such as animal and plant remains and excrement into inorganic substances, returning them to the inorganic environment for reuse, thus maintaining ecosystem material cycles and energy flow.
"The relationship between biodiversity and ecosystem function is one of the focal points in international ecology in recent years," said co-corresponding author Liu Shirong to China Science Daily. It is generally believed both domestically and abroad that higher biodiversity leads to stronger ecosystem functionality and stability, particularly in resistance to stress or extreme climates.
"However, most domestic and foreign research has focused on the relationship between productivity (i.e., plant growth) and biodiversity, and it is unclear whether changes in biodiversity affect ecosystem function at different trophic levels," said Liu Shirong.
Junwei Luan, the first author and co-corresponding author of the paper, told China Science Daily that the decomposition process is an ecological process controlled by multiple trophic levels. The decomposition of forest litter is one of the most important processes in terrestrial ecosystems, determining carbon and nutrient cycling in ecosystems, affecting community structure and dynamics, and thus influencing ecosystem function.
When litter is decomposed by microorganisms, the organic carbon it contains is converted into carbon dioxide and released into the atmosphere. Therefore, "litter decomposition affects the carbon feedback between the atmosphere and the biosphere, thereby affecting climate change," said Junwei Luan. On the other hand, large amounts of mineral elements such as nitrogen, phosphorus, and potassium are released during the decomposition process, becoming important sources of soil nutrients.
In recent years, global climate warming has become increasingly severe, and drought directly affects terrestrial ecosystems, leading to a significant decline in ecosystem functionality and stability. It is widely believed in academia that biodiversity may help improve the resistance and resilience of ecosystems, thereby mitigating the impact of climate change.
Cross-Regional, Cross-Type: Massive Data Analysis
From 2013 to 2016, during his study abroad, Junwei Luan focused on how biodiversity in northern peatland ecosystems affects greenhouse gas emission regulation processes.
In 2016, after returning to China, Junwei Luan learned that Chinese scientists engaged in forest ecology research had successively established ecosystem positioning observation research stations in five climate zones in China, including temperate, warm temperate, subtropical, and tropical zones, relying on departments such as the State Forestry Administration and the Chinese Academy of Sciences. Forest drought simulation experiments were conducted, and each experimental platform was established and maintained by scientists spontaneously raising research funds through various channels. These independent platforms together formed a networked experiment—the Forest Climate Drought Simulation Network Research Platform.
This experiment diverted a portion of the rainfall penetrating the forest to areas outside the plots, reducing the rainfall received within the plots and creating a certain degree of drought stress. The aim was to study and reveal the response mechanisms and mechanisms of forest ecosystem processes and functions in different regions of China to potential future climate droughts.
"This experiment provides an excellent platform for verifying relevant scientific issues. Especially with the increasingly severe problems of global climate warming causing aridification and drought, threatening the health and service functions of forest ecosystems," said Junwei Luan. The theoretical exploration of whether forest biodiversity can effectively mitigate the effects of drought can provide valuable references for future forest ecosystem management.
So, he quickly contacted the relevant platform leaders and began to systematically study the important process of litter decomposition that affects carbon and nutrient cycling in forest ecosystems.
"The biodiversity affecting litter decomposition mainly includes the diversity of litter itself and the diversity of decomposers," said Liu Shirong.
To this end, the experiment, based on setting gradients of litter richness, used litter decomposition bags with different mesh sizes to separate and analyze the complexity of decomposer functional groups and their communities. A total of 1,620 decomposition bags were set up for this study, conducting decomposition experiments with different leaf litter compositions.
"The biggest challenge was the large sample size, large workload, and difficulty in separation," said Junwei Luan. Over a thousand decomposition bags contained 2 to 4 different types of leaf litter. These litters were left to decompose in the field for a period before being retrieved to the laboratory, where each bag's leaf litter was sorted by species, separated, dried, weighed, and elemental content measured.
This was a massive undertaking. Reviewers noted that the experimental design was impressive, and the amount of work invested was unimaginable. Therefore, the scale of the experiment makes the results of this study applicable to ecosystems worldwide.
The results revealed that in different forest types, simulated drought reduced the degradation of carbon and particularly nitrogen elements during litter decomposition, while the diversity of litter and the complexity of decomposer communities alleviated the negative effects of drought on these biogeochemical cycles. Forest management has introduced new biodiversity initiatives. Junwei Luan explains that firstly, the complexity of decomposer communities alleviates the negative impact of drought on carbon and nitrogen cycling, especially soil macrofauna (such as millipedes and isopods) participating in decomposition processes can compensate for the effects of drought on microbially driven decomposition.
Secondly, as the richness of litter species increases, the complementary diversity effects (i.e., the more species, the higher the decomposition rate, exceeding simple additivity, known as complementarity effects) increase accordingly. Compared to lower litter species richness, higher species richness can more effectively offset the effects of drought.
Finally, as climate conditions become drier, the mitigating effect of biodiversity on ecosystem functions shows robustness and predictability across different forest types, aiding in adaptive management measures to address the impacts of climate change.
"In the process of artificially creating or modifying ecosystems, introducing higher biodiversity can effectively enhance the resistance of such ecosystems to climate change such as drought. Similarly, in arid environments, a system with high biodiversity can effectively resist drought and other stresses, thereby providing more habitats and environments for other organisms, forming a positive feedback loop for biodiversity conservation," says Shirong Liu.
"This provides a reference for forest management departments," says Junwei Luan. In the future, in the process of afforestation or the transformation of inefficient artificial forests, on the one hand, consideration can be given to mixed planting of tree species, shrubs, and grasses to increase plant diversity. On the other hand, the complexity of decomposer communities can be increased to stabilize the functioning of the ecosystem.
For forest management departments, promoting plant diversity and complex decomposer communities is conducive to maintaining the functionality and stability of forest ecosystems under future climate conditions and can enhance forest resilience.
However, Junwei Luan emphasizes that the directly measured impacts in the study underestimate the importance of litter structure and chemical diversity, as it can also promote the complexity and richness of decomposers, thereby potentially producing a greater overall impact on litter diversity.
"In the long run, the distribution of species, community composition, and the abundance of related species will all be influenced by climate change. Changes in litter composition and decomposer community complexity influenced by these changes will alter the mitigation effects reported in current studies, depending on the direction and extent of future changes in these components," says Junwei Luan.
Related paper information: https://doi.org/10.1073/pnas.2313334121
