Hawaii data key in CO2, plant adap­ta­tion find­ing

Honolulu Star-Advertiser - - LOCAL - By Michael Tsai mt­sai@starad­ver­tiser.com

While hu­mans may yet be at a loss for how to re­spond to ris­ing car­bon diox­ide lev­els, a new study sug­gests that plants have al­ready adapted. Us­ing data col­lected from Mauna Loa Ob­ser­va­tory and the South Pole, re­searchers from the Scripps In­sti­tu­tion of Oceanog­ra­phy and the Univer­sity of Cal­i­for­nia at San Diego ex­am­ined changes in CO2 lev­els since 1978 and cor­re­spond­ing changes in plant be­hav­ior, con­clud­ing that land plants have be­come more ef­fi­cient at us­ing wa­ter for pho­to­syn­the­sis. The re­sults of the study were pub­lished in the Sept. 11 edi­tion of the jour­nal Pro­ceed­ings of the Na­tional Acad­emy of Sciences.

As the re­searchers note, CO2 lev­els have risen since the late 19th cen­tury due at least in part to hu­man ac­tiv­ity. Ac­cord­ingly, the ra­tio of the two main atomic forms of car­bon — car­bon-12 and car­bon-13 — has de­creased. The sci­en­tists cited the low 13C-to-12C ra­tio associated with fos­sil fuel com­bus­tion as one of the causes. Up­dat­ing the record of CO2 iso­topic ra­tios made at Scripps nearly 40 years ago, re­searchers con­firmed that a dis­crep­ancy ex­isted be­tween pro­jected changes based on hu­man ac­tiv­ity and nat­u­ral fac­tors and the ac­tual mea­sured changes. They fur­ther de­ter­mined that the only plau­si­ble ex­pla­na­tion for the dis­crep­ancy was that there was a change in how much wa­ter plants needed to grow. This con­clu­sion was based on the un­der­stand­ing that higher lev­els of CO2 af­fect the be­hav­ior of stom­ata, the mi­cro­scopic holes in leaves that al­low plants to take up CO2 and lose wa­ter in evap­o­ra­tion. With higher CO2 lev­els, plants can have smaller or fewer stom­ata, thereby al­low­ing for more pho­to­syn­the­sis with the same amount of wa­ter. The find­ings sup­port a long-held no­tion by plant bi­ol­o­gists that plants can achieve an op­ti­mum re­sponse to in­creases in at­mo­spheric CO2. Fur­ther, the greater ef­fi­ciency in pho­to­syn­the­sis points to the abil­ity of plants to re­move more CO2 from the at­mos­phere, thereby par­tially off­set­ting some ef­fects of cli­mate change caused by hu­man ac­tiv­ity.

How­ever, lead au­thor Ralph Keel­ing cau­tioned that such ben­e­fit has to be weighed against other neg­a­tive changes like ex­treme weather, bio­di­ver­sity loss and sea-level rise. Keel­ing is the son of Charles D. “Dave” Keel­ing, a Scripps re­searcher who be­gan tak­ing C02 read­ings atop Mauna Loa in 1958. His find­ings took the form of the Keel­ing Curve, which shows an in­ex­orable rise in at­mo­spheric car­bon, with sea­sonal vari­a­tions.

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