Ecological significance of marcescence in Himalayan plants: Why is standing dead phytomass more important in demanding, resource-limited environments?

Understanding mechanisms allowing plants to thrive in challenging
conditions is critical for predicting their responses to global
environmental change. An often overlooked ecological adaptation is
marcescence, where leaves and stems are retained beyond their typical
shedding time, with implications for nutrient recycling and carbon
sequestration. Marcescence may be common in plants with conservative
resource-use strategies, especially in environments with limited resources
and marked seasonality, such as deserts and alpine regions. However, the
extent to which marcescence occurs in different taxa across different
habitats and its relationship to seasonality and plant functioning as
reflected in ecophysiological traits remains understudied. We studied 600
individuals across 40 Himalayan herb species found in desert, steppe,
alpine, and subnival habitats, spanning 3000 to 5400 m elevation.
Marcescence was observed in 37 out of 40 species evaluated, with 57% of
the sampled individuals displaying dead phytomass, indicating the
widespread nature of this phenomenon in Himalayan ecosystems. Environment
and plant traits emerged as significant factors influencing the amount of
dead-standing biomass. These findings remained robust after accounting for
intraspecific variation and phylogenetic inertia. Desert and steppe
species exhibited greater marcescent biomass, characterized by tenfold
more dead stem biomass than alpine and subnival plants. In contrast, the
proportion of dead phytomass increased with elevation due to increased
dead leaf fraction. Tall desert species with heavily lignified stems and
limited nitrogen and phosphorus content had high levels of stem
marcescence, which may aid litter photodegradation and nutrient recycling
but also deter herbivory and promote seed dispersal (tumbleweed).
Conversely, slow-growing alpine and subnival plants with higher water-use
efficiency, foliar C:N ratios, and parenchymatic storage tissue rich in
mobile carbohydrates had a high proportion of marcescent leaves, which may
aid survival in these resource-limited environments by providing delayed
nutrients through moisture-conserving mulch that also provides insulation
and protection from frost. This study provides new insights into the
complex interplay of habitat, seasonality, and plant traits in dead
phytomass retention in Himalayan plants. Marcescence is prevalent in
resource-conservative species in highly seasonal, resource-limited
habitats and may significantly shape the functioning and biodiversity of
Himalayan ecosystems.