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Resistance of tropical seedlings to drought is mediated by neighbourhood diversity

Michael J. O’Brien, Glen Reynolds, Robert Ong and Andy Hector

Occasional periods of drought are typical of most tropical forests, but climate change is increasing drought frequency and intensity in many areas across the globe, threatening the structure and function of these ecosystems. The effects of intermittent drought on tropical tree communities remain poorly understood and the potential impacts of intensified drought under future climatic conditions are even less well known. The response of forests to altered precipitation will be determined by the tolerances of different species to reduced water availability and the interactions among plants that alleviate or exacerbate the effects of drought. Here, we report the response of experimental monocultures and mixtures of tropical trees to simulated drought, which reveals a fundamental shift in the nature of interactions among species. Weaker competition for water in diverse communities allowed seedlings to maintain growth under drought while more intense competition among conspecifics inhibited growth under the same conditions. These results show that reduced competition for water among species in mixtures mediates community resistance to drought. The delayed onset of competition for water among species in more diverse neighbourhoods during drought has potential implications for the coexistence of species in tropical forests and the resilience of these systems to climate change.

Seedling water stress under rainfall and neighbourhood treatments. Physiological response of seedlings to drought (red) and ever-wet (blue) conditions in mixture, non-sibling and sibling neighbourhoods.  Leaf water potentials (95% CI) were significantly lower under drought for non-sibling and sibling neighbourhoods (n = 24 for each neighbourhood × rainfall treatment), but the leaf water potential was statistically indistinguishable between the drought and ever-wet conditions for species mixtures.

https://www.nature.com/articles/s41559-017-0326-0.epdf?shared_access_token=OS3nDTwUHCGZPEkNT0ONZ9RgN0jAjWel9jnR3ZoTv0Ns6fP1WzQNck9TanMo7CFZ8qbT6OnejiT_GlI5KRwG2WCKIWSJXBthfUfrDAljFgdVelMA5PyirIAUFxEPDBrMxa3iA9m5pe_OAzt6WbAYbY_o60hCZtOHomiu-nPjlRo%3D

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https://www.webislam.com/media/2012/07/54112_la_revolucion_de_una_brizna_de_paja.pdf

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The Secrets of the Wood Wide Web 

By  Robert Macfarlane

"...For centuries, fungi were widely held to be harmful to plants, parasites that cause disease and dysfunction. More recently, it has become understood that certain kinds of common fungi exist in subtle symbiosis with plants, bringing about not infection but connection.These fungi send out gossamer-fine fungal tubes called hyphae, which infiltrate the soil and weave into the tips of plant roots at a cellular level. Roots and fungi combine to form what is called a mycorrhiza: itself a growing-together of the Greek words for fungus (mykós) and root (riza). In this way, individual plants are joined to one another by an underground hyphal network: a dazzlingly complex and collaborative structure that has become known as the Wood Wide Web.

...The relationship between these mycorrhizal fungi and the plants they connect is now known to be ancient (around four hundred and fifty million years old) and largely one of mutualism —a subset of symbiosis in which both organisms benefit from their association. In the case of the mycorrhizae, the fungi siphon off food from the trees, taking some of the carbon-rich sugar that they produce during photosynthesis. The plants, in turn, obtain nutrients such as phosphorus and nitrogen that the fungi have acquired from the soil, by means of enzymes that the trees do not possess.

The implications of the Wood Wide Web far exceed this basic exchange of goods between plant and fungi, however. The fungal network also allows plants to distribute resources—sugar, nitrogen, and phosphorus—between one another. A dying tree might divest itself of its resources to the benefit of the community, for example, or a young seedling in a heavily shaded understory might be supported with extra resources by its stronger neighbors. Even more remarkably, the network also allows plants to send one another warnings. A plant under attack from aphids can indicate to a nearby plant that it should raise its defensive response before the aphids reach it..."

https://www.newyorker.com/tech/elements/the-secrets-of-the-wood-wide-web/amp

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