Heng Ge, Institute of Botany of the Chinese Academy of Sciences, discusses her article: Autumn nutrient resorption and twig storage shape spring phenology in woody species
When we think about spring phenology, we usually notice the visible signs first: buds swelling, leaves unfolding, and flowers opening. Spring phenology is often discussed as a response to temperature, but our study suggests that spring growth is not driven by climate alone. What a plant stores inside its own tissues during the previous autumn may also help determine how early it starts spring growth.
This idea started with a simple question: what happens to nutrients when leaves senesce? Before leaves fall, plants withdraw part of their nitrogen and phosphorus and move these nutrients into longer-lived tissues. This process, known as nutrient resorption, is a classic nutrient conservation strategy. What interested us was what happened after that. Are these nutrients stored in twigs? And if so, could this internal nutrient storage influence the timing of spring bud break and leaf-out?
To answer these questions, we worked in the China National Botanical Garden, where we studied 20 woody species with a wide range of leaf traits, including shrubs, broadleaved trees, and conifers. We sampled branches during the peak growing season and again in late autumn, after leaf senescence, to measure how much nitrogen and phosphorus had been withdrawn from leaves and how much had accumulated in living twigs. At the same time, we tracked phenology in the field: when leaves began to fall in autumn, how long leaf fall lasted, when buds broke in spring, and how long leaf-out took.
We found that species with more acquisitive traits – those associated with faster resource use – tended to have higher nutrient resorption from leaves. These species also showed greater nutrient accumulation in twigs, particularly for phosphorus. This pattern suggests that twigs may serve as important storage organs during the dormant season.
We also found that internal nutrient dynamics were tied to phenology in both autumn and spring. In autumn, species that shed their leaves later and over a shorter period tended to show higher phosphorus resorption efficiency. In spring, the pattern became even more striking. Species with higher twig nutrient accumulation tended to break bud earlier and maintain a longer leaf-out period.
This is important because early spring is a challenging time for plants. Air temperatures may be rising, but soil temperatures can still be low, and roots may not yet be taking up nutrients efficiently. Under those conditions, stored nutrients in twigs may provide a critical internal supply, helping plants support bud development and new tissue growth before the soil becomes a reliable source of nutrients again.
These findings also have broader ecological significance. If internal nutrient storage helps species leaf out earlier or sustain longer spring development, then internal nutrient cycling may influence the length of the growing season, plant performance, and ultimately ecosystem functioning. It also suggests that species differ not only in when they grow, but in how they prepare to grow.
There is still much to learn. Our study focused on nitrogen and phosphorus in leaves and twigs, but other nutrients and other woody tissues may also be important. Future experiments that manipulate nutrient availability or senescence conditions will be needed to test these causal links directly.
Still, our study highlights a clear conclusion: spring phenology may not be controlled only by external cues such as temperature. It may also depend on how effectively plants recycled and stored nutrients during the previous autumn.
