How will plants adapt to climate change?

The 400-hectare wild­fire in Roses in late Feb­ru­ary is an ex­am­ple of what ex­perts fear: ir­reg­u­lar rain­fall mak­ing the land arid enough that dry veg­e­ta­tion ac­cu­mu­lates and acts as fuel, mean­ing for­est fires can occur at any time of the year, not just in the sum­mer.

The main im­pacts we will see in Cat­alo­nia are drought and water stress, ac­cord­ing to the Cata­lan Strat­egy for Adap­ta­tion to Cli­mate Change. It re­mains to be seen how hu­mans will cope, but the nat­ural en­vi­ron­ment will have to adapt too. The Uni­ver­sity of Girona’s (UdG) Mediter­ranean Soils and Veg­e­ta­tion Re­search Group is study­ing how this will af­fect Mediter­ranean ter­res­trial ecosys­tems.

“Plants need a lot of water. The car­bon diox­ide (CO2) re­quired for pho­to­syn­the­sis pen­e­trates the leaves through struc­tures called stom­ata, which open and close. When the plant lacks CO2, the stom­ata open, but while CO2 en­ters, water exits,” says Do­lors Verda­guer, mem­ber of the re­search group and pro­fes­sor of the UdG’s De­part­ment of En­vi­ron­men­tal Sci­ences.

This process, known as tran­spi­ra­tion, hap­pens a lot in plants. “I al­ways tell my stu­dents that they’re like water pumps: they take water from the ground and put it into the at­mos­phere. If they have water, nu­tri­ents, CO2 and light, then they grow. If they don’t have water, the cells don’t mul­ti­ply. In ad­di­tion, if the stom­ata are not suf­fi­ciently hy­drated, they relax and close, and the plant doesn’t get enough CO2 and can­not per­form pho­to­syn­the­sis. This also stops growth,” she says. Dur­ing a drought, the plant can die if it has con­sumed all its water re­serves.

Yet cer­tain plants can adapt some fea­tures so as not to reach this ex­treme. This is al­ready the case in the Mediter­ranean, which usu­ally has water in the spring, al­low­ing plants to grow that can then with­stand high tem­per­a­tures and drought in the sum­mer. Among the adap­ta­tions is de­vel­op­ing hard, long-last­ing leaves, while these adap­ta­tions can also be mod­u­lated by leaves get­ting smaller, for ex­am­ple. “If the leaf size is re­duced, there’s less sur­face area to tran­spire,” adds Verda­guer. An­other strat­egy is to de­velop thicker, more wa­ter­proof leaves to pre­vent tran­spi­ra­tion through the cu­ti­cle, the pro­tec­tive layer that cov­ers the leaf. Also, smaller, thicker leaves have more nat­ural poly­mers that help main­tain their shape even if the plant is de­hy­drated. For ex­am­ple, if we dry a spinach leaf, it will wither and won’t re­gain func­tion­al­ity. Yet if we do the same with an oak leaf, its struc­ture will be main­tained and, if it gets water again, it can re­gain its func­tion.

There are many stud­ies on how cli­mate change will af­fect veg­e­ta­tion, but most focus on agri­cul­tural plants. The UdG is specif­i­cally study­ing plants we have here. “We al­ready have a good idea about what will hap­pen. Plants will adapt if they can, but if there is a very se­vere drought, mor­tal­ity will in­evitably in­crease,” says Verda­guer, who also notes the ef­fects of ul­tra­vi­o­let (UV) rays.

“More pe­ri­ods of drought are pre­dicted, which means more days of sun­shine, and so more ul­tra­vi­o­let ra­di­a­tion, UV-A and UV-B ra­di­a­tion, will reach the at­mos­phere. Our stud­ies on this show that plants will have to adapt,” she adds, point­ing out that some will do bet­ter than oth­ers. Dif­fer­ent species have been shown to de­velop dif­fer­ent strate­gies. For ex­am­ple: the straw­berry tree keeps its stom­ata open more dur­ing drought con­di­tions, which may favour it be­cause it will grow more than more con­ser­v­a­tive species. “In the long run, there may be changes in the plants due to com­pe­ti­tion be­tween them,” says Verda­guer.

“More pe­ri­ods of drought are pre­dicted, which means more days of sun­shine, and so more ul­tra­vi­o­let ra­di­a­tion, UV-A and UV-B ra­di­a­tion, will reach the at­mos­phere. Our stud­ies on this show that plants will have to adapt,” she adds, point­ing out that some will do bet­ter than oth­ers. Dif­fer­ent species have been shown to de­velop dif­fer­ent strate­gies. For ex­am­ple: the straw­berry tree keeps its stom­ata open more dur­ing drought con­di­tions, which may favour it be­cause it will grow more than more con­ser­v­a­tive species. “In the long run, there may be changes in the plants due to com­pe­ti­tion be­tween them,” says Verda­guer.