03 March 2023

Éagsúlacht Speiceas Plandaí

Méadaíonn éagsúlacht níos airde speiceas plandaí flúirse na bpríomhghéinte a bhaineann le ráta athraithe fosfar na hithreach. Aaron Mac an tSionnaigh, Taighdeoir Iardhochtúireachta, Teagasc gCaisleán Bhaile Sheáin

Is gné riachtanach é fosfar (P) le haghaidh fás plandaí agus táirgiúlacht i gcórais féaraigh. San ithir, áfach, faightear P go hiondúil i bhfoirmeacha neamhorgánacha faoi cheangal (m.sh. fosfáit chailciam) nó i bhfoirmeacha casta orgánacha a bhfuil nasc an-chobhsaí Carbóin (C) – P acu (m.sh. fosfónáití). Tá foirmeacha fosfair den sórt sin róchasta do phlandaí a ghlacadh trína gcuid fréamhacha. Chun é seo a chomhrac, is minic a chuirtear P (fosfáit neamhorgánach) atá ar fáil don phlanda leo mar leasachán neamhorgánach. Coinníonn sé seo táirgeacht leordhóthanacha, ach is féidir le caillteanais uisce agus imní chomhshaoil ghaolmhar a bheith bainteach leis.

Tá raidhse baictéar ag plandaí a bhaineann lena bhfréamhstruchtúir. Tá sé ríthábhachtach go bhfuil grúpaí baictéaracha áirithe in ann P, atá faoi cheangalgo neamhorgánach nó go horgánach, a bhriseadh síos go foirmeacha atá ar fáil don phlanda . Bíonn géin (gcd) ag roinnt baictéar ar trína mheán sin a dhéantar glúcós a ocsaídiú go haigéad glúcócach ar féidir leis ceangal le mianraí ithreach, amhail cailciam, agus a scaoileann P atá faoi cheangal. Is féidir le baictéir ithreach an bhraisle géine phn a iompar freisin, ina bhfuil raon géinte i gceist maidir le hidrealú an naisc chobhsaí C – P a fhaightear i bhfosfónáití. Is réimse gníomhach taighde é leas a bhaint as próisis bhaictéaracha dá leithéid chun an P atá ar fáil don phlanda i gcórais féaraigh a mhéadú.

Meicníocht a bhfuil gealladh faoi agus a d’fhéadfadh a bheith ann chun é seo a bhaint amach ná trí éagsúlacht speiceas plandaí a mhéadú laistigh de bháinseacha féaraigh, mar go bhfuil dea-dhoiciméadú déanta ar éifeachtaí éagsúlachta plandaí ar tháirgeacht bhithmhaise a mhéadú. Scrúdaigh taighde ag Teagasc i gCaisleán Bhaile Sheáin éagsúlacht mhéadaitheach speiceas plandaí thar raon leibhéal (1, 2, 4, 8, 16 agus 60 speiceas) agus an tionchar a imríonn sé ar fhlúirse mheasta na bpríomhghéinte a bhaineann le ráta athraithe ithir P. Léirigh na torthaí méadú láidir ar raidhse na géine gcd le méadú ar éagsúlacht speiceas plandaí. Chomh maith leis sin, mhéadaigh ocht ngéin a fuarthas laistigh den bhraisle géinte phn le méadú ar éagsúlacht speiceas plandaí. Léiríonn na torthaí seo gur féidir le héagsúlacht níos airde speiceas plandaí cur le cumas na mbaictéar ithreach cineálacha sonracha P nach bhfuil ar fáil don phlanda a spreagadh. D’fhéadfadh meicníochtaí den sórt sin a bheith ríthábhachtach chun úsáid leasacháin neamhorgánacha P ar chórais féaraigh a laghdú, rud a fheabhsódh a n-inbhuanaitheacht comhshaoil.

Higher plant species diversity increases the abundance of key genes involved in soil phosphorus turnover  

By Aaron Fox, Postdoctoral Researcher, Johnstown Castle Research Centre

Phosphorus (P) is an essential element for plant growth and productivity in grassland systems. In soil, however, P is typically found in either inorganically bound forms (e.g. calcium phosphate) or in complex organic forms with a very stable Carbon (C) – P bond (e.g., phosphonates). Such forms of phosphorus are too complex for plants to uptake through their roots. To counteract this, plant available P (inorganic phosphate) is often added as an inorganic fertilizer. This maintains adequate yields, but can be associated with losses to water and associated environmental concerns.

Plants have a plethora of bacteria associated with their root structures. Crucially, certain bacterial groups are capable of breaking down either inorganically or organically bound P to plant available forms. Some bacteria harbour a gene (gcd) which mediates the oxidation of glucose to gluconic acid which can bind to soil minerals, such as calcium, and release bound P. Soil bacteria can also harbour the phn gene cluster, which contains a range of genes involved in the hydrolysis of the stable C – P bond found in phosphonates. Harnessing such bacterial processes to increase plant available P in grassland systems is an active area of research.

A promising potential mechanism to achieve this is through increasing plant species diversity within grassland swards, as plant diversity effects on increasing biomass yields have been well-documented. Research at Teagasc Johnstown Castle examined increasing plant species diversity across a range of levels (1, 2, 4, 8, 16 and 60 species) and its influence on the estimated abundance of key genes involved in soil P turnover. The results showed a strong increase in the abundance of the gcd gene with increasing plant species diversity. Also, eight genes found within the phn gene cluster also increased with increasing plant species diversity. These results demonstrate that higher plant species diversity can enhance the potential of soil bacteria to mobilize specific forms of plant unavailable P. Such mechanisms may be key to reducing P inorganic fertilizer application to grassland systems, improving their environmental sustainability.