The critical role of plant phenology in the biomass production of alpine plants under climate change

Miaojun Ma, Gansu Gannan Grassland Ecosystem National Observation and Research Station, State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Ecology, Lanzhou University, discusses his article: Asynchronous phenological responses to warming affect biomass production contrastingly in flowering functional groups

Background

Plant phenology and productivity changes represent two of the most critical climate-induced changes in alpine ecosystems. Recent studies have consistently reported trends of earlier spring phenological events, including leaf emergence and flowering, in response to climate warming. Such shifts in phenology affect plant growth and subsequently impact productivity. Warming leading to earlier spring vegetation growth can either promote summer height by increasing carbon sequestration or hinder it by consuming resources crucial for later growth stages. However, the response of alpine plant phenology to climate change and its consequences on plant height growth and biomass productivity remain unclear.

We examined the effects of warming and changes in precipitation on leaf emergence and reproductive phenology, plant height at different phenological stages, height growth rate, and biomass production between flowering functional groups from 2021 to 2023, based on a seven year long field experiment with warming and altered precipitation from a long-term nitrogen addition experiment in Gansu Gannan Grassland Ecosystem National Observation and Research Station located in an alpine meadow on the eastern Tibetan Plateau.

Hypotheses

We asked two questions:

(1) How do warming and altered precipitation affect alpine plant phenology, height growth patterns, and biomass production?

(2) Do phenological changes in different flowering functional groups regulate their growth and biomass production? If so, what mechanisms underlie these regulatory effects?

Key findings

We found that warming differentially affected the height growth rates of alpine plants during their reproductive stages between flowering functional groups, and that asynchronous responses of reproductive phenology to warming further mediated warming effects on biomass production. Specifically, for early-spring flowering (ESF) plants, warming advanced spring phenology and increased plant height growth rate between leaf emergence and flowering, but constrained height growth rate in the later fruiting period, thereby reducing their biomass production. In contrast, for mid-summer flowering (MSF) plants, warming consistently advanced both vegetative and reproductive phenological events and promoted plant height growth rate throughout the growing season, ultimately increasing biomass production.

Our findings suggest that future climate warming will induce asynchronous phenological responses among flowering functional groups in alpine meadows, resulting in contrasting effects on their biomass production and ultimately impacting the species composition and stability of plant communities.

Temperature and water availability are crucial drivers of biomass production in alpine plants. Our results highlight that the relative importance of these specific drivers differs between flowering functional groups. Warming reduces biomass in early-spring flowering plants, but enhances both maximum plant height and biomass production of mid-summer flowering plants. Furthermore, warming effects on the plant biomass production for flowering functional groups were mediated by alterations in leaf emergence and other reproductive phenological events.

Implications

Overall, alpine plant community biomass production remains unchanged under long-term climate warming, at least partially due to the opposite responses of early- and late-flowering functional groups in their biomass production response to warming. Therefore, future studies should consider the crucial role of plant phenology in shaping alpine plant growth dynamics and biomass production, particularly the differences among flowering functional groups.

Our results suggest that warming, either directly or indirectly through altered plant phenology, decreases the biomass of early-flowering plants while enhancing that of late-flowering plants. These findings have several key implications. Firstly, phenological response and height growth strategies vary among flowering functional groups in alpine meadows. Secondly, warming differently altered phenology and biomass production in early- and late-season plants, potentially creating new ecological niches and enabling species invasion. Thirdly, the complex links between phenology and growth/biomass underscore the need for a comprehensive understanding of the full life cycle under climate change. Overall, these insights enrich our understanding of alpine plant growth dynamics in climate change, highlighting the crucial role of phenological shifts in biomass production.

Plant productivity is determined by both the growth rate and the timing of plant growth. However, plant growth and phenology are also influenced by other environmental factors, such as photoperiod, nutrient availability, and grazing intensity. Thus, future research should take into account the combined effects of multiple climatic and anthropogenic factors on alpine plant productivity. Additionally, cryptic phenology is increasingly recognized as closely linked to plant material cycling and may further influence plant biomass accumulation. Integrating growth rate with cryptic phenology could thus enhance our understanding of alpine ecosystem functioning under climate change.

For more from Miaojun Ma, see previous posts here and here.